This file is indexed.

/usr/share/pyshared/sqlalchemy/sql/expression.py is in python-sqlalchemy 0.7.8-1.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

   1
   2
   3
   4
   5
   6
   7
   8
   9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
  24
  25
  26
  27
  28
  29
  30
  31
  32
  33
  34
  35
  36
  37
  38
  39
  40
  41
  42
  43
  44
  45
  46
  47
  48
  49
  50
  51
  52
  53
  54
  55
  56
  57
  58
  59
  60
  61
  62
  63
  64
  65
  66
  67
  68
  69
  70
  71
  72
  73
  74
  75
  76
  77
  78
  79
  80
  81
  82
  83
  84
  85
  86
  87
  88
  89
  90
  91
  92
  93
  94
  95
  96
  97
  98
  99
 100
 101
 102
 103
 104
 105
 106
 107
 108
 109
 110
 111
 112
 113
 114
 115
 116
 117
 118
 119
 120
 121
 122
 123
 124
 125
 126
 127
 128
 129
 130
 131
 132
 133
 134
 135
 136
 137
 138
 139
 140
 141
 142
 143
 144
 145
 146
 147
 148
 149
 150
 151
 152
 153
 154
 155
 156
 157
 158
 159
 160
 161
 162
 163
 164
 165
 166
 167
 168
 169
 170
 171
 172
 173
 174
 175
 176
 177
 178
 179
 180
 181
 182
 183
 184
 185
 186
 187
 188
 189
 190
 191
 192
 193
 194
 195
 196
 197
 198
 199
 200
 201
 202
 203
 204
 205
 206
 207
 208
 209
 210
 211
 212
 213
 214
 215
 216
 217
 218
 219
 220
 221
 222
 223
 224
 225
 226
 227
 228
 229
 230
 231
 232
 233
 234
 235
 236
 237
 238
 239
 240
 241
 242
 243
 244
 245
 246
 247
 248
 249
 250
 251
 252
 253
 254
 255
 256
 257
 258
 259
 260
 261
 262
 263
 264
 265
 266
 267
 268
 269
 270
 271
 272
 273
 274
 275
 276
 277
 278
 279
 280
 281
 282
 283
 284
 285
 286
 287
 288
 289
 290
 291
 292
 293
 294
 295
 296
 297
 298
 299
 300
 301
 302
 303
 304
 305
 306
 307
 308
 309
 310
 311
 312
 313
 314
 315
 316
 317
 318
 319
 320
 321
 322
 323
 324
 325
 326
 327
 328
 329
 330
 331
 332
 333
 334
 335
 336
 337
 338
 339
 340
 341
 342
 343
 344
 345
 346
 347
 348
 349
 350
 351
 352
 353
 354
 355
 356
 357
 358
 359
 360
 361
 362
 363
 364
 365
 366
 367
 368
 369
 370
 371
 372
 373
 374
 375
 376
 377
 378
 379
 380
 381
 382
 383
 384
 385
 386
 387
 388
 389
 390
 391
 392
 393
 394
 395
 396
 397
 398
 399
 400
 401
 402
 403
 404
 405
 406
 407
 408
 409
 410
 411
 412
 413
 414
 415
 416
 417
 418
 419
 420
 421
 422
 423
 424
 425
 426
 427
 428
 429
 430
 431
 432
 433
 434
 435
 436
 437
 438
 439
 440
 441
 442
 443
 444
 445
 446
 447
 448
 449
 450
 451
 452
 453
 454
 455
 456
 457
 458
 459
 460
 461
 462
 463
 464
 465
 466
 467
 468
 469
 470
 471
 472
 473
 474
 475
 476
 477
 478
 479
 480
 481
 482
 483
 484
 485
 486
 487
 488
 489
 490
 491
 492
 493
 494
 495
 496
 497
 498
 499
 500
 501
 502
 503
 504
 505
 506
 507
 508
 509
 510
 511
 512
 513
 514
 515
 516
 517
 518
 519
 520
 521
 522
 523
 524
 525
 526
 527
 528
 529
 530
 531
 532
 533
 534
 535
 536
 537
 538
 539
 540
 541
 542
 543
 544
 545
 546
 547
 548
 549
 550
 551
 552
 553
 554
 555
 556
 557
 558
 559
 560
 561
 562
 563
 564
 565
 566
 567
 568
 569
 570
 571
 572
 573
 574
 575
 576
 577
 578
 579
 580
 581
 582
 583
 584
 585
 586
 587
 588
 589
 590
 591
 592
 593
 594
 595
 596
 597
 598
 599
 600
 601
 602
 603
 604
 605
 606
 607
 608
 609
 610
 611
 612
 613
 614
 615
 616
 617
 618
 619
 620
 621
 622
 623
 624
 625
 626
 627
 628
 629
 630
 631
 632
 633
 634
 635
 636
 637
 638
 639
 640
 641
 642
 643
 644
 645
 646
 647
 648
 649
 650
 651
 652
 653
 654
 655
 656
 657
 658
 659
 660
 661
 662
 663
 664
 665
 666
 667
 668
 669
 670
 671
 672
 673
 674
 675
 676
 677
 678
 679
 680
 681
 682
 683
 684
 685
 686
 687
 688
 689
 690
 691
 692
 693
 694
 695
 696
 697
 698
 699
 700
 701
 702
 703
 704
 705
 706
 707
 708
 709
 710
 711
 712
 713
 714
 715
 716
 717
 718
 719
 720
 721
 722
 723
 724
 725
 726
 727
 728
 729
 730
 731
 732
 733
 734
 735
 736
 737
 738
 739
 740
 741
 742
 743
 744
 745
 746
 747
 748
 749
 750
 751
 752
 753
 754
 755
 756
 757
 758
 759
 760
 761
 762
 763
 764
 765
 766
 767
 768
 769
 770
 771
 772
 773
 774
 775
 776
 777
 778
 779
 780
 781
 782
 783
 784
 785
 786
 787
 788
 789
 790
 791
 792
 793
 794
 795
 796
 797
 798
 799
 800
 801
 802
 803
 804
 805
 806
 807
 808
 809
 810
 811
 812
 813
 814
 815
 816
 817
 818
 819
 820
 821
 822
 823
 824
 825
 826
 827
 828
 829
 830
 831
 832
 833
 834
 835
 836
 837
 838
 839
 840
 841
 842
 843
 844
 845
 846
 847
 848
 849
 850
 851
 852
 853
 854
 855
 856
 857
 858
 859
 860
 861
 862
 863
 864
 865
 866
 867
 868
 869
 870
 871
 872
 873
 874
 875
 876
 877
 878
 879
 880
 881
 882
 883
 884
 885
 886
 887
 888
 889
 890
 891
 892
 893
 894
 895
 896
 897
 898
 899
 900
 901
 902
 903
 904
 905
 906
 907
 908
 909
 910
 911
 912
 913
 914
 915
 916
 917
 918
 919
 920
 921
 922
 923
 924
 925
 926
 927
 928
 929
 930
 931
 932
 933
 934
 935
 936
 937
 938
 939
 940
 941
 942
 943
 944
 945
 946
 947
 948
 949
 950
 951
 952
 953
 954
 955
 956
 957
 958
 959
 960
 961
 962
 963
 964
 965
 966
 967
 968
 969
 970
 971
 972
 973
 974
 975
 976
 977
 978
 979
 980
 981
 982
 983
 984
 985
 986
 987
 988
 989
 990
 991
 992
 993
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
3593
3594
3595
3596
3597
3598
3599
3600
3601
3602
3603
3604
3605
3606
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
3619
3620
3621
3622
3623
3624
3625
3626
3627
3628
3629
3630
3631
3632
3633
3634
3635
3636
3637
3638
3639
3640
3641
3642
3643
3644
3645
3646
3647
3648
3649
3650
3651
3652
3653
3654
3655
3656
3657
3658
3659
3660
3661
3662
3663
3664
3665
3666
3667
3668
3669
3670
3671
3672
3673
3674
3675
3676
3677
3678
3679
3680
3681
3682
3683
3684
3685
3686
3687
3688
3689
3690
3691
3692
3693
3694
3695
3696
3697
3698
3699
3700
3701
3702
3703
3704
3705
3706
3707
3708
3709
3710
3711
3712
3713
3714
3715
3716
3717
3718
3719
3720
3721
3722
3723
3724
3725
3726
3727
3728
3729
3730
3731
3732
3733
3734
3735
3736
3737
3738
3739
3740
3741
3742
3743
3744
3745
3746
3747
3748
3749
3750
3751
3752
3753
3754
3755
3756
3757
3758
3759
3760
3761
3762
3763
3764
3765
3766
3767
3768
3769
3770
3771
3772
3773
3774
3775
3776
3777
3778
3779
3780
3781
3782
3783
3784
3785
3786
3787
3788
3789
3790
3791
3792
3793
3794
3795
3796
3797
3798
3799
3800
3801
3802
3803
3804
3805
3806
3807
3808
3809
3810
3811
3812
3813
3814
3815
3816
3817
3818
3819
3820
3821
3822
3823
3824
3825
3826
3827
3828
3829
3830
3831
3832
3833
3834
3835
3836
3837
3838
3839
3840
3841
3842
3843
3844
3845
3846
3847
3848
3849
3850
3851
3852
3853
3854
3855
3856
3857
3858
3859
3860
3861
3862
3863
3864
3865
3866
3867
3868
3869
3870
3871
3872
3873
3874
3875
3876
3877
3878
3879
3880
3881
3882
3883
3884
3885
3886
3887
3888
3889
3890
3891
3892
3893
3894
3895
3896
3897
3898
3899
3900
3901
3902
3903
3904
3905
3906
3907
3908
3909
3910
3911
3912
3913
3914
3915
3916
3917
3918
3919
3920
3921
3922
3923
3924
3925
3926
3927
3928
3929
3930
3931
3932
3933
3934
3935
3936
3937
3938
3939
3940
3941
3942
3943
3944
3945
3946
3947
3948
3949
3950
3951
3952
3953
3954
3955
3956
3957
3958
3959
3960
3961
3962
3963
3964
3965
3966
3967
3968
3969
3970
3971
3972
3973
3974
3975
3976
3977
3978
3979
3980
3981
3982
3983
3984
3985
3986
3987
3988
3989
3990
3991
3992
3993
3994
3995
3996
3997
3998
3999
4000
4001
4002
4003
4004
4005
4006
4007
4008
4009
4010
4011
4012
4013
4014
4015
4016
4017
4018
4019
4020
4021
4022
4023
4024
4025
4026
4027
4028
4029
4030
4031
4032
4033
4034
4035
4036
4037
4038
4039
4040
4041
4042
4043
4044
4045
4046
4047
4048
4049
4050
4051
4052
4053
4054
4055
4056
4057
4058
4059
4060
4061
4062
4063
4064
4065
4066
4067
4068
4069
4070
4071
4072
4073
4074
4075
4076
4077
4078
4079
4080
4081
4082
4083
4084
4085
4086
4087
4088
4089
4090
4091
4092
4093
4094
4095
4096
4097
4098
4099
4100
4101
4102
4103
4104
4105
4106
4107
4108
4109
4110
4111
4112
4113
4114
4115
4116
4117
4118
4119
4120
4121
4122
4123
4124
4125
4126
4127
4128
4129
4130
4131
4132
4133
4134
4135
4136
4137
4138
4139
4140
4141
4142
4143
4144
4145
4146
4147
4148
4149
4150
4151
4152
4153
4154
4155
4156
4157
4158
4159
4160
4161
4162
4163
4164
4165
4166
4167
4168
4169
4170
4171
4172
4173
4174
4175
4176
4177
4178
4179
4180
4181
4182
4183
4184
4185
4186
4187
4188
4189
4190
4191
4192
4193
4194
4195
4196
4197
4198
4199
4200
4201
4202
4203
4204
4205
4206
4207
4208
4209
4210
4211
4212
4213
4214
4215
4216
4217
4218
4219
4220
4221
4222
4223
4224
4225
4226
4227
4228
4229
4230
4231
4232
4233
4234
4235
4236
4237
4238
4239
4240
4241
4242
4243
4244
4245
4246
4247
4248
4249
4250
4251
4252
4253
4254
4255
4256
4257
4258
4259
4260
4261
4262
4263
4264
4265
4266
4267
4268
4269
4270
4271
4272
4273
4274
4275
4276
4277
4278
4279
4280
4281
4282
4283
4284
4285
4286
4287
4288
4289
4290
4291
4292
4293
4294
4295
4296
4297
4298
4299
4300
4301
4302
4303
4304
4305
4306
4307
4308
4309
4310
4311
4312
4313
4314
4315
4316
4317
4318
4319
4320
4321
4322
4323
4324
4325
4326
4327
4328
4329
4330
4331
4332
4333
4334
4335
4336
4337
4338
4339
4340
4341
4342
4343
4344
4345
4346
4347
4348
4349
4350
4351
4352
4353
4354
4355
4356
4357
4358
4359
4360
4361
4362
4363
4364
4365
4366
4367
4368
4369
4370
4371
4372
4373
4374
4375
4376
4377
4378
4379
4380
4381
4382
4383
4384
4385
4386
4387
4388
4389
4390
4391
4392
4393
4394
4395
4396
4397
4398
4399
4400
4401
4402
4403
4404
4405
4406
4407
4408
4409
4410
4411
4412
4413
4414
4415
4416
4417
4418
4419
4420
4421
4422
4423
4424
4425
4426
4427
4428
4429
4430
4431
4432
4433
4434
4435
4436
4437
4438
4439
4440
4441
4442
4443
4444
4445
4446
4447
4448
4449
4450
4451
4452
4453
4454
4455
4456
4457
4458
4459
4460
4461
4462
4463
4464
4465
4466
4467
4468
4469
4470
4471
4472
4473
4474
4475
4476
4477
4478
4479
4480
4481
4482
4483
4484
4485
4486
4487
4488
4489
4490
4491
4492
4493
4494
4495
4496
4497
4498
4499
4500
4501
4502
4503
4504
4505
4506
4507
4508
4509
4510
4511
4512
4513
4514
4515
4516
4517
4518
4519
4520
4521
4522
4523
4524
4525
4526
4527
4528
4529
4530
4531
4532
4533
4534
4535
4536
4537
4538
4539
4540
4541
4542
4543
4544
4545
4546
4547
4548
4549
4550
4551
4552
4553
4554
4555
4556
4557
4558
4559
4560
4561
4562
4563
4564
4565
4566
4567
4568
4569
4570
4571
4572
4573
4574
4575
4576
4577
4578
4579
4580
4581
4582
4583
4584
4585
4586
4587
4588
4589
4590
4591
4592
4593
4594
4595
4596
4597
4598
4599
4600
4601
4602
4603
4604
4605
4606
4607
4608
4609
4610
4611
4612
4613
4614
4615
4616
4617
4618
4619
4620
4621
4622
4623
4624
4625
4626
4627
4628
4629
4630
4631
4632
4633
4634
4635
4636
4637
4638
4639
4640
4641
4642
4643
4644
4645
4646
4647
4648
4649
4650
4651
4652
4653
4654
4655
4656
4657
4658
4659
4660
4661
4662
4663
4664
4665
4666
4667
4668
4669
4670
4671
4672
4673
4674
4675
4676
4677
4678
4679
4680
4681
4682
4683
4684
4685
4686
4687
4688
4689
4690
4691
4692
4693
4694
4695
4696
4697
4698
4699
4700
4701
4702
4703
4704
4705
4706
4707
4708
4709
4710
4711
4712
4713
4714
4715
4716
4717
4718
4719
4720
4721
4722
4723
4724
4725
4726
4727
4728
4729
4730
4731
4732
4733
4734
4735
4736
4737
4738
4739
4740
4741
4742
4743
4744
4745
4746
4747
4748
4749
4750
4751
4752
4753
4754
4755
4756
4757
4758
4759
4760
4761
4762
4763
4764
4765
4766
4767
4768
4769
4770
4771
4772
4773
4774
4775
4776
4777
4778
4779
4780
4781
4782
4783
4784
4785
4786
4787
4788
4789
4790
4791
4792
4793
4794
4795
4796
4797
4798
4799
4800
4801
4802
4803
4804
4805
4806
4807
4808
4809
4810
4811
4812
4813
4814
4815
4816
4817
4818
4819
4820
4821
4822
4823
4824
4825
4826
4827
4828
4829
4830
4831
4832
4833
4834
4835
4836
4837
4838
4839
4840
4841
4842
4843
4844
4845
4846
4847
4848
4849
4850
4851
4852
4853
4854
4855
4856
4857
4858
4859
4860
4861
4862
4863
4864
4865
4866
4867
4868
4869
4870
4871
4872
4873
4874
4875
4876
4877
4878
4879
4880
4881
4882
4883
4884
4885
4886
4887
4888
4889
4890
4891
4892
4893
4894
4895
4896
4897
4898
4899
4900
4901
4902
4903
4904
4905
4906
4907
4908
4909
4910
4911
4912
4913
4914
4915
4916
4917
4918
4919
4920
4921
4922
4923
4924
4925
4926
4927
4928
4929
4930
4931
4932
4933
4934
4935
4936
4937
4938
4939
4940
4941
4942
4943
4944
4945
4946
4947
4948
4949
4950
4951
4952
4953
4954
4955
4956
4957
4958
4959
4960
4961
4962
4963
4964
4965
4966
4967
4968
4969
4970
4971
4972
4973
4974
4975
4976
4977
4978
4979
4980
4981
4982
4983
4984
4985
4986
4987
4988
4989
4990
4991
4992
4993
4994
4995
4996
4997
4998
4999
5000
5001
5002
5003
5004
5005
5006
5007
5008
5009
5010
5011
5012
5013
5014
5015
5016
5017
5018
5019
5020
5021
5022
5023
5024
5025
5026
5027
5028
5029
5030
5031
5032
5033
5034
5035
5036
5037
5038
5039
5040
5041
5042
5043
5044
5045
5046
5047
5048
5049
5050
5051
5052
5053
5054
5055
5056
5057
5058
5059
5060
5061
5062
5063
5064
5065
5066
5067
5068
5069
5070
5071
5072
5073
5074
5075
5076
5077
5078
5079
5080
5081
5082
5083
5084
5085
5086
5087
5088
5089
5090
5091
5092
5093
5094
5095
5096
5097
5098
5099
5100
5101
5102
5103
5104
5105
5106
5107
5108
5109
5110
5111
5112
5113
5114
5115
5116
5117
5118
5119
5120
5121
5122
5123
5124
5125
5126
5127
5128
5129
5130
5131
5132
5133
5134
5135
5136
5137
5138
5139
5140
5141
5142
5143
5144
5145
5146
5147
5148
5149
5150
5151
5152
5153
5154
5155
5156
5157
5158
5159
5160
5161
5162
5163
5164
5165
5166
5167
5168
5169
5170
5171
5172
5173
5174
5175
5176
5177
5178
5179
5180
5181
5182
5183
5184
5185
5186
5187
5188
5189
5190
5191
5192
5193
5194
5195
5196
5197
5198
5199
5200
5201
5202
5203
5204
5205
5206
5207
5208
5209
5210
5211
5212
5213
5214
5215
5216
5217
5218
5219
5220
5221
5222
5223
5224
5225
5226
5227
5228
5229
5230
5231
5232
5233
5234
5235
5236
5237
5238
5239
5240
5241
5242
5243
5244
5245
5246
5247
5248
5249
5250
5251
5252
5253
5254
5255
5256
5257
5258
5259
5260
5261
5262
5263
5264
5265
5266
5267
5268
5269
5270
5271
5272
5273
5274
5275
5276
5277
5278
5279
5280
5281
5282
5283
5284
5285
5286
5287
5288
5289
5290
5291
5292
5293
5294
5295
5296
5297
5298
5299
5300
5301
5302
5303
5304
5305
5306
5307
5308
5309
5310
5311
5312
5313
5314
5315
5316
5317
5318
5319
5320
5321
5322
5323
5324
5325
5326
5327
5328
5329
5330
5331
5332
5333
5334
5335
5336
5337
5338
5339
5340
5341
5342
5343
5344
5345
5346
5347
5348
5349
5350
5351
5352
5353
5354
5355
5356
5357
5358
5359
5360
5361
5362
5363
5364
5365
5366
5367
5368
5369
5370
5371
5372
5373
5374
5375
5376
5377
5378
5379
5380
5381
5382
5383
5384
5385
5386
5387
5388
5389
5390
5391
5392
5393
5394
5395
5396
5397
5398
5399
5400
5401
5402
5403
5404
5405
5406
5407
5408
5409
5410
5411
5412
5413
5414
5415
5416
5417
5418
5419
5420
5421
5422
5423
5424
5425
5426
5427
5428
5429
5430
5431
5432
5433
5434
5435
5436
5437
5438
5439
5440
5441
5442
5443
5444
5445
5446
5447
5448
5449
5450
5451
5452
5453
5454
5455
5456
5457
5458
5459
5460
5461
5462
5463
5464
5465
5466
5467
5468
5469
5470
5471
5472
5473
5474
5475
5476
5477
5478
5479
5480
5481
5482
5483
5484
5485
5486
5487
5488
5489
5490
5491
5492
5493
5494
5495
5496
5497
5498
5499
5500
5501
5502
5503
5504
5505
5506
5507
5508
5509
5510
5511
5512
5513
5514
5515
5516
5517
5518
5519
5520
5521
5522
5523
5524
5525
5526
5527
5528
5529
5530
5531
5532
5533
5534
5535
5536
5537
5538
5539
5540
5541
5542
5543
5544
5545
5546
5547
5548
5549
5550
5551
5552
5553
5554
5555
5556
5557
5558
5559
5560
5561
5562
5563
5564
5565
5566
5567
5568
5569
5570
5571
5572
5573
5574
5575
5576
5577
5578
5579
5580
5581
5582
5583
5584
5585
5586
5587
5588
5589
5590
5591
5592
5593
5594
5595
5596
5597
5598
5599
5600
5601
5602
5603
5604
5605
5606
5607
5608
5609
5610
5611
5612
5613
5614
5615
5616
5617
5618
5619
5620
5621
5622
5623
5624
5625
5626
5627
5628
5629
5630
5631
5632
5633
5634
5635
5636
5637
5638
5639
5640
5641
5642
5643
5644
5645
5646
5647
5648
5649
5650
5651
5652
5653
5654
5655
5656
5657
5658
5659
5660
5661
5662
5663
5664
5665
5666
5667
5668
5669
5670
5671
5672
5673
5674
5675
5676
5677
5678
5679
5680
5681
5682
5683
5684
5685
5686
5687
5688
5689
5690
5691
5692
5693
5694
5695
5696
5697
5698
# sql/expression.py
# Copyright (C) 2005-2012 the SQLAlchemy authors and contributors <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php

"""Defines the base components of SQL expression trees.

All components are derived from a common base class
:class:`.ClauseElement`.  Common behaviors are organized
based on class hierarchies, in some cases via mixins.

All object construction from this package occurs via functions which
in some cases will construct composite :class:`.ClauseElement` structures
together, and in other cases simply return a single :class:`.ClauseElement`
constructed directly.  The function interface affords a more "DSL-ish"
feel to constructing SQL expressions and also allows future class
reorganizations.

Even though classes are not constructed directly from the outside,
most classes which have additional public methods are considered to be
public (i.e. have no leading underscore).  Other classes which are
"semi-public" are marked with a single leading underscore; these
classes usually have few or no public methods and are less guaranteed
to stay the same in future releases.

"""

import itertools, re
from operator import attrgetter

from sqlalchemy import util, exc
from sqlalchemy.sql import operators
from sqlalchemy.sql.operators import Operators, ColumnOperators
from sqlalchemy.sql.visitors import Visitable, cloned_traverse
import operator

functions = util.importlater("sqlalchemy.sql", "functions")
sqlutil = util.importlater("sqlalchemy.sql", "util")
sqltypes = util.importlater("sqlalchemy", "types")
default = util.importlater("sqlalchemy.engine", "default")

__all__ = [
    'Alias', 'ClauseElement', 'ColumnCollection', 'ColumnElement',
    'CompoundSelect', 'Delete', 'FromClause', 'Insert', 'Join', 'Select',
    'Selectable', 'TableClause', 'Update', 'alias', 'and_', 'asc', 'between',
    'bindparam', 'case', 'cast', 'column', 'delete', 'desc', 'distinct',
    'except_', 'except_all', 'exists', 'extract', 'func', 'modifier',
    'collate', 'insert', 'intersect', 'intersect_all', 'join', 'label',
    'literal', 'literal_column', 'not_', 'null', 'nullsfirst', 'nullslast',
    'or_', 'outparam', 'outerjoin', 'over', 'select', 'subquery', 'table', 'text',
    'tuple_', 'type_coerce', 'union', 'union_all', 'update', ]

PARSE_AUTOCOMMIT = util.symbol('PARSE_AUTOCOMMIT')

def nullsfirst(column):
    """Return a NULLS FIRST ``ORDER BY`` clause element.

    e.g.::

      someselect.order_by(desc(table1.mycol).nullsfirst())

    produces::

      ORDER BY mycol DESC NULLS FIRST

    """
    return _UnaryExpression(column, modifier=operators.nullsfirst_op)

def nullslast(column):
    """Return a NULLS LAST ``ORDER BY`` clause element.

    e.g.::

      someselect.order_by(desc(table1.mycol).nullslast())

    produces::

        ORDER BY mycol DESC NULLS LAST

    """
    return _UnaryExpression(column, modifier=operators.nullslast_op)

def desc(column):
    """Return a descending ``ORDER BY`` clause element.

    e.g.::

      someselect.order_by(desc(table1.mycol))

    produces::

        ORDER BY mycol DESC

    """
    return _UnaryExpression(column, modifier=operators.desc_op)

def asc(column):
    """Return an ascending ``ORDER BY`` clause element.

    e.g.::

      someselect.order_by(asc(table1.mycol))

    produces::

      ORDER BY mycol ASC

    """
    return _UnaryExpression(column, modifier=operators.asc_op)

def outerjoin(left, right, onclause=None):
    """Return an ``OUTER JOIN`` clause element.

    The returned object is an instance of :class:`.Join`.

    Similar functionality is also available via the 
    :meth:`~.FromClause.outerjoin()` method on any 
    :class:`.FromClause`.

    :param left: The left side of the join.

    :param right: The right side of the join.

    :param onclause:  Optional criterion for the ``ON`` clause, is 
      derived from foreign key relationships established between 
      left and right otherwise.

    To chain joins together, use the :meth:`.FromClause.join` or 
    :meth:`.FromClause.outerjoin` methods on the resulting 
    :class:`.Join` object.

    """
    return Join(left, right, onclause, isouter=True)

def join(left, right, onclause=None, isouter=False):
    """Return a ``JOIN`` clause element (regular inner join).

    The returned object is an instance of :class:`.Join`.

    Similar functionality is also available via the 
    :meth:`~.FromClause.join()` method on any 
    :class:`.FromClause`.

    :param left: The left side of the join.

    :param right: The right side of the join.

    :param onclause:  Optional criterion for the ``ON`` clause, is 
      derived from foreign key relationships established between 
      left and right otherwise.

    To chain joins together, use the :meth:`.FromClause.join` or 
    :meth:`.FromClause.outerjoin` methods on the resulting 
    :class:`.Join` object.


    """
    return Join(left, right, onclause, isouter)

def select(columns=None, whereclause=None, from_obj=[], **kwargs):
    """Returns a ``SELECT`` clause element.

    Similar functionality is also available via the :func:`select()`
    method on any :class:`.FromClause`.

    The returned object is an instance of :class:`.Select`.

    All arguments which accept :class:`.ClauseElement` arguments also accept
    string arguments, which will be converted as appropriate into
    either :func:`text()` or :func:`literal_column()` constructs.

    See also:

    :ref:`coretutorial_selecting` - Core Tutorial description of :func:`.select`.

    :param columns:
      A list of :class:`.ClauseElement` objects, typically
      :class:`.ColumnElement` objects or subclasses, which will form the
      columns clause of the resulting statement. For all members which are
      instances of :class:`.Selectable`, the individual :class:`.ColumnElement`
      members of the :class:`.Selectable` will be added individually to the
      columns clause. For example, specifying a
      :class:`~sqlalchemy.schema.Table` instance will result in all the
      contained :class:`~sqlalchemy.schema.Column` objects within to be added
      to the columns clause.

      This argument is not present on the form of :func:`select()`
      available on :class:`~sqlalchemy.schema.Table`.

    :param whereclause:
      A :class:`.ClauseElement` expression which will be used to form the
      ``WHERE`` clause.

    :param from_obj:
      A list of :class:`.ClauseElement` objects which will be added to the
      ``FROM`` clause of the resulting statement. Note that "from" objects are
      automatically located within the columns and whereclause ClauseElements.
      Use this parameter to explicitly specify "from" objects which are not
      automatically locatable. This could include
      :class:`~sqlalchemy.schema.Table` objects that aren't otherwise present,
      or :class:`.Join` objects whose presence will supercede that of the
      :class:`~sqlalchemy.schema.Table` objects already located in the other
      clauses.

    :param autocommit:
      Deprecated.  Use .execution_options(autocommit=<True|False>)
      to set the autocommit option.

    :param bind=None:
      an :class:`~.base.Engine` or :class:`~.base.Connection` instance 
      to which the
      resulting :class:`.Select` object will be bound.  The :class:`.Select`
      object will otherwise automatically bind to whatever
      :class:`~.base.Connectable` instances can be located within its contained
      :class:`.ClauseElement` members.

    :param correlate=True:
      indicates that this :class:`.Select` object should have its
      contained :class:`.FromClause` elements "correlated" to an enclosing
      :class:`.Select` object.  This means that any :class:`.ClauseElement`
      instance within the "froms" collection of this :class:`.Select`
      which is also present in the "froms" collection of an
      enclosing select will not be rendered in the ``FROM`` clause
      of this select statement.

    :param distinct=False:
      when ``True``, applies a ``DISTINCT`` qualifier to the columns
      clause of the resulting statement.

      The boolean argument may also be a column expression or list
      of column expressions - this is a special calling form which
      is understood by the Postgresql dialect to render the
      ``DISTINCT ON (<columns>)`` syntax.

      ``distinct`` is also available via the :meth:`~.Select.distinct`
      generative method.

      .. note:: 
      
         The ``distinct`` keyword's acceptance of a string
         argument for usage with MySQL is deprecated.  Use
         the ``prefixes`` argument or :meth:`~.Select.prefix_with`.

    :param for_update=False:
      when ``True``, applies ``FOR UPDATE`` to the end of the
      resulting statement.  
      
      Certain database dialects also support
      alternate values for this parameter:
      
      * With the MySQL dialect, the value ``"read"`` translates to 
        ``LOCK IN SHARE MODE``.
      * With the Oracle and Postgresql dialects, the value ``"nowait"``
        translates to ``FOR UPDATE NOWAIT``.
      * With the Postgresql dialect, the values "read" and ``"read_nowait"``
        translate to ``FOR SHARE`` and ``FOR SHARE NOWAIT``, respectively.

        .. versionadded:: 0.7.7

    :param group_by:
      a list of :class:`.ClauseElement` objects which will comprise the
      ``GROUP BY`` clause of the resulting select.

    :param having:
      a :class:`.ClauseElement` that will comprise the ``HAVING`` clause
      of the resulting select when ``GROUP BY`` is used.

    :param limit=None:
      a numerical value which usually compiles to a ``LIMIT``
      expression in the resulting select.  Databases that don't
      support ``LIMIT`` will attempt to provide similar
      functionality.

    :param offset=None:
      a numeric value which usually compiles to an ``OFFSET``
      expression in the resulting select.  Databases that don't
      support ``OFFSET`` will attempt to provide similar
      functionality.

    :param order_by:
      a scalar or list of :class:`.ClauseElement` objects which will
      comprise the ``ORDER BY`` clause of the resulting select.

    :param prefixes:
      a list of strings or :class:`.ClauseElement` objects to include
      directly after the SELECT keyword in the generated statement,
      for dialect-specific query features.  ``prefixes`` is
      also available via the :meth:`~.Select.prefix_with`
      generative method.

    :param use_labels=False:
      when ``True``, the statement will be generated using labels
      for each column in the columns clause, which qualify each
      column with its parent table's (or aliases) name so that name
      conflicts between columns in different tables don't occur.
      The format of the label is <tablename>_<column>.  The "c"
      collection of the resulting :class:`.Select` object will use these
      names as well for targeting column members.

      use_labels is also available via the :meth:`~._SelectBase.apply_labels`
      generative method.

    """
    return Select(columns, whereclause=whereclause, from_obj=from_obj,
                  **kwargs)

def subquery(alias, *args, **kwargs):
    """Return an :class:`.Alias` object derived 
    from a :class:`.Select`.

    name
      alias name

    \*args, \**kwargs

      all other arguments are delivered to the
      :func:`select` function.

    """
    return Select(*args, **kwargs).alias(alias)

def insert(table, values=None, inline=False, **kwargs):
    """Represent an ``INSERT`` statement via the :class:`.Insert` SQL 
    construct.

    Similar functionality is available via the :meth:`~.TableClause.insert` method on
    :class:`~.schema.Table`.


    :param table: The table to be inserted into.

    :param values: A dictionary which specifies the column specifications of
     the ``INSERT``, and is optional. If left as None, the column
     specifications are determined from the bind parameters used during the
     compile phase of the ``INSERT`` statement. If the bind parameters also
     are None during the compile phase, then the column specifications will be
     generated from the full list of table columns. Note that the
     :meth:`~Insert.values()` generative method may also be used for this.

    :param prefixes: A list of modifier keywords to be inserted between INSERT
      and INTO. Alternatively, the :meth:`~Insert.prefix_with` generative
      method may be used.

    :param inline: if True, SQL defaults will be compiled 'inline' into the
      statement and not pre-executed.

    If both `values` and compile-time bind parameters are present, the
    compile-time bind parameters override the information specified
    within `values` on a per-key basis.

    The keys within `values` can be either :class:`~sqlalchemy.schema.Column`
    objects or their string identifiers. Each key may reference one of:

    * a literal data value (i.e. string, number, etc.);
    * a Column object;
    * a SELECT statement.

    If a ``SELECT`` statement is specified which references this
    ``INSERT`` statement's table, the statement will be correlated
    against the ``INSERT`` statement.

    See also:

        :ref:`coretutorial_insert_expressions` - SQL Expression Tutorial

        :ref:`inserts_and_updates` - SQL Expression Tutorial

    """
    return Insert(table, values, inline=inline, **kwargs)

def update(table, whereclause=None, values=None, inline=False, **kwargs):
    """Represent an ``UPDATE`` statement via the :class:`.Update` SQL 
    construct.

    E.g.::

        from sqlalchemy import update
        
        stmt = update(users).where(users.c.id==5).\\
                values(name='user #5')

    Similar functionality is available via the :meth:`~.TableClause.update` method on
    :class:`.Table`::
    
        
        stmt = users.update().\\
                    where(users.c.id==5).\\
                    values(name='user #5')

    :param table: A :class:`.Table` object representing the database
     table to be updated.

    :param whereclause: Optional SQL expression describing the ``WHERE``
     condition of the ``UPDATE`` statement.   Modern applications
     may prefer to use the generative :meth:`~Update.where()` 
     method to specify the ``WHERE`` clause.
     
     The WHERE clause can refer to multiple tables.
     For databases which support this, an ``UPDATE FROM`` clause will
     be generated, or on MySQL, a multi-table update.  The statement 
     will fail on databases that don't have support for multi-table
     update statements.  A SQL-standard method of referring to
     additional tables in the WHERE clause is to use a correlated
     subquery::
     
        users.update().values(name='ed').where(
                users.c.name==select([addresses.c.email_address]).\\
                            where(addresses.c.user_id==users.c.id).\\
                            as_scalar()
                )

     .. versionchanged:: 0.7.4
         The WHERE clause can refer to multiple tables.

    :param values:
      Optional dictionary which specifies the ``SET`` conditions of the
      ``UPDATE``.  If left as ``None``, the ``SET``
      conditions are determined from those parameters passed to the 
      statement during the execution and/or compilation of the 
      statement.   When compiled standalone without any parameters,
      the ``SET`` clause generates for all columns.
      
      Modern applications may prefer to use the generative 
      :meth:`.Update.values` method to set the values of the 
      UPDATE statement.

    :param inline:
      if True, SQL defaults present on :class:`.Column` objects via 
      the ``default`` keyword will be compiled 'inline' into the statement
      and not pre-executed.  This means that their values will not
      be available in the dictionary returned from 
      :meth:`.ResultProxy.last_updated_params`.

    If both ``values`` and compile-time bind parameters are present, the
    compile-time bind parameters override the information specified
    within ``values`` on a per-key basis.

    The keys within ``values`` can be either :class:`.Column`
    objects or their string identifiers (specifically the "key" of the
    :class:`.Column`, normally but not necessarily equivalent to
    its "name").  Normally, the
    :class:`.Column` objects used here are expected to be
    part of the target :class:`.Table` that is the table 
    to be updated.  However when using MySQL, a multiple-table
    UPDATE statement can refer to columns from any of
    the tables referred to in the WHERE clause.
    
    The values referred to in ``values`` are typically:
    
    * a literal data value (i.e. string, number, etc.)
    * a SQL expression, such as a related :class:`.Column`,
      a scalar-returning :func:`.select` construct, 
      etc.

    When combining :func:`.select` constructs within the values
    clause of an :func:`.update` construct,
    the subquery represented by the :func:`.select` should be 
    *correlated* to the parent table, that is, providing criterion
    which links the table inside the subquery to the outer table
    being updated::
    
        users.update().values(
                name=select([addresses.c.email_address]).\\
                        where(addresses.c.user_id==users.c.id).\\
                        as_scalar()
            )

    See also:

        :ref:`inserts_and_updates` - SQL Expression 
        Language Tutorial
    
    
    """
    return Update(
            table, 
            whereclause=whereclause, 
            values=values, 
            inline=inline, 
            **kwargs)

def delete(table, whereclause = None, **kwargs):
    """Represent a ``DELETE`` statement via the :class:`.Delete` SQL 
    construct.

    Similar functionality is available via the :meth:`~.TableClause.delete` method on
    :class:`~.schema.Table`.

    :param table: The table to be updated.

    :param whereclause: A :class:`.ClauseElement` describing the ``WHERE``
      condition of the ``UPDATE`` statement. Note that the
      :meth:`~Delete.where()` generative method may be used instead.

    See also:
    
        :ref:`deletes` - SQL Expression Tutorial

    """
    return Delete(table, whereclause, **kwargs)

def and_(*clauses):
    """Join a list of clauses together using the ``AND`` operator.

    The ``&`` operator is also overloaded on all
    :class:`_CompareMixin` subclasses to produce the
    same result.

    """
    if len(clauses) == 1:
        return clauses[0]
    return BooleanClauseList(operator=operators.and_, *clauses)

def or_(*clauses):
    """Join a list of clauses together using the ``OR`` operator.

    The ``|`` operator is also overloaded on all
    :class:`_CompareMixin` subclasses to produce the
    same result.

    """
    if len(clauses) == 1:
        return clauses[0]
    return BooleanClauseList(operator=operators.or_, *clauses)

def not_(clause):
    """Return a negation of the given clause, i.e. ``NOT(clause)``.

    The ``~`` operator is also overloaded on all
    :class:`_CompareMixin` subclasses to produce the
    same result.

    """
    return operators.inv(_literal_as_binds(clause))

def distinct(expr):
    """Return a ``DISTINCT`` clause.

    e.g.::

        distinct(a)

    renders::

        DISTINCT a

    """
    expr = _literal_as_binds(expr)
    return _UnaryExpression(expr, operator=operators.distinct_op, type_=expr.type)

def between(ctest, cleft, cright):
    """Return a ``BETWEEN`` predicate clause.

    Equivalent of SQL ``clausetest BETWEEN clauseleft AND clauseright``.

    The :func:`between()` method on all
    :class:`_CompareMixin` subclasses provides
    similar functionality.

    """
    ctest = _literal_as_binds(ctest)
    return ctest.between(cleft, cright)


def case(whens, value=None, else_=None):
    """Produce a ``CASE`` statement.

    whens
      A sequence of pairs, or alternatively a dict,
      to be translated into "WHEN / THEN" clauses.

    value
      Optional for simple case statements, produces
      a column expression as in "CASE <expr> WHEN ..."

    else\_
      Optional as well, for case defaults produces
      the "ELSE" portion of the "CASE" statement.

    The expressions used for THEN and ELSE,
    when specified as strings, will be interpreted
    as bound values. To specify textual SQL expressions
    for these, use the :func:`literal_column`
    construct. 

    The expressions used for the WHEN criterion
    may only be literal strings when "value" is
    present, i.e. CASE table.somecol WHEN "x" THEN "y".
    Otherwise, literal strings are not accepted
    in this position, and either the text(<string>)
    or literal(<string>) constructs must be used to
    interpret raw string values.

    Usage examples::

      case([(orderline.c.qty > 100, item.c.specialprice),
            (orderline.c.qty > 10, item.c.bulkprice)
          ], else_=item.c.regularprice)
      case(value=emp.c.type, whens={
              'engineer': emp.c.salary * 1.1,
              'manager':  emp.c.salary * 3,
          })

    Using :func:`literal_column()`, to allow for databases that
    do not support bind parameters in the ``then`` clause.  The type
    can be specified which determines the type of the :func:`case()` construct
    overall::

        case([(orderline.c.qty > 100, 
                literal_column("'greaterthan100'", String)),
              (orderline.c.qty > 10, literal_column("'greaterthan10'",
                String))
            ], else_=literal_column("'lethan10'", String))

    """

    return _Case(whens, value=value, else_=else_)

def cast(clause, totype, **kwargs):
    """Return a ``CAST`` function.

    Equivalent of SQL ``CAST(clause AS totype)``.

    Use with a :class:`~sqlalchemy.types.TypeEngine` subclass, i.e::

      cast(table.c.unit_price * table.c.qty, Numeric(10,4))

    or::

      cast(table.c.timestamp, DATE)

    """
    return _Cast(clause, totype, **kwargs)

def extract(field, expr):
    """Return the clause ``extract(field FROM expr)``."""

    return _Extract(field, expr)

def collate(expression, collation):
    """Return the clause ``expression COLLATE collation``.

    e.g.::

        collate(mycolumn, 'utf8_bin')

    produces::

        mycolumn COLLATE utf8_bin

    """

    expr = _literal_as_binds(expression)
    return _BinaryExpression(
        expr, 
        _literal_as_text(collation), 
        operators.collate, type_=expr.type)

def exists(*args, **kwargs):
    """Return an ``EXISTS`` clause as applied to a :class:`.Select` object.

    Calling styles are of the following forms::

        # use on an existing select()
        s = select([table.c.col1]).where(table.c.col2==5)
        s = exists(s)

        # construct a select() at once
        exists(['*'], **select_arguments).where(criterion)

        # columns argument is optional, generates "EXISTS (SELECT *)"
        # by default.
        exists().where(table.c.col2==5)

    """
    return _Exists(*args, **kwargs)

def union(*selects, **kwargs):
    """Return a ``UNION`` of multiple selectables.

    The returned object is an instance of
    :class:`.CompoundSelect`.

    A similar :func:`union()` method is available on all
    :class:`.FromClause` subclasses.

    \*selects
      a list of :class:`.Select` instances.

    \**kwargs
       available keyword arguments are the same as those of
       :func:`select`.

    """
    return CompoundSelect(CompoundSelect.UNION, *selects, **kwargs)

def union_all(*selects, **kwargs):
    """Return a ``UNION ALL`` of multiple selectables.

    The returned object is an instance of
    :class:`.CompoundSelect`.

    A similar :func:`union_all()` method is available on all
    :class:`.FromClause` subclasses.

    \*selects
      a list of :class:`.Select` instances.

    \**kwargs
      available keyword arguments are the same as those of
      :func:`select`.

    """
    return CompoundSelect(CompoundSelect.UNION_ALL, *selects, **kwargs)

def except_(*selects, **kwargs):
    """Return an ``EXCEPT`` of multiple selectables.

    The returned object is an instance of
    :class:`.CompoundSelect`.

    \*selects
      a list of :class:`.Select` instances.

    \**kwargs
      available keyword arguments are the same as those of
      :func:`select`.

    """
    return CompoundSelect(CompoundSelect.EXCEPT, *selects, **kwargs)

def except_all(*selects, **kwargs):
    """Return an ``EXCEPT ALL`` of multiple selectables.

    The returned object is an instance of
    :class:`.CompoundSelect`.

    \*selects
      a list of :class:`.Select` instances.

    \**kwargs
      available keyword arguments are the same as those of
      :func:`select`.

    """
    return CompoundSelect(CompoundSelect.EXCEPT_ALL, *selects, **kwargs)

def intersect(*selects, **kwargs):
    """Return an ``INTERSECT`` of multiple selectables.

    The returned object is an instance of
    :class:`.CompoundSelect`.

    \*selects
      a list of :class:`.Select` instances.

    \**kwargs
      available keyword arguments are the same as those of
      :func:`select`.

    """
    return CompoundSelect(CompoundSelect.INTERSECT, *selects, **kwargs)

def intersect_all(*selects, **kwargs):
    """Return an ``INTERSECT ALL`` of multiple selectables.

    The returned object is an instance of
    :class:`.CompoundSelect`.

    \*selects
      a list of :class:`.Select` instances.

    \**kwargs
      available keyword arguments are the same as those of
      :func:`select`.

    """
    return CompoundSelect(CompoundSelect.INTERSECT_ALL, *selects, **kwargs)

def alias(selectable, name=None):
    """Return an :class:`.Alias` object.

    An :class:`.Alias` represents any :class:`.FromClause`
    with an alternate name assigned within SQL, typically using the ``AS``
    clause when generated, e.g. ``SELECT * FROM table AS aliasname``.

    Similar functionality is available via the 
    :meth:`~.FromClause.alias` method
    available on all :class:`.FromClause` subclasses.

    When an :class:`.Alias` is created from a :class:`.Table` object,
    this has the effect of the table being rendered
    as ``tablename AS aliasname`` in a SELECT statement.

    For :func:`.select` objects, the effect is that of creating a named
    subquery, i.e. ``(select ...) AS aliasname``.

    The ``name`` parameter is optional, and provides the name
    to use in the rendered SQL.  If blank, an "anonymous" name
    will be deterministically generated at compile time.
    Deterministic means the name is guaranteed to be unique against
    other constructs used in the same statement, and will also be the
    same name for each successive compilation of the same statement
    object.

    :param selectable: any :class:`.FromClause` subclass,
        such as a table, select statement, etc.

    :param name: string name to be assigned as the alias.
        If ``None``, a name will be deterministically generated
        at compile time.

    """
    return Alias(selectable, name=name)


def literal(value, type_=None):
    """Return a literal clause, bound to a bind parameter.

    Literal clauses are created automatically when non- :class:`.ClauseElement`
    objects (such as strings, ints, dates, etc.) are used in a comparison
    operation with a :class:`_CompareMixin`
    subclass, such as a :class:`~sqlalchemy.schema.Column` object. Use this function to force the
    generation of a literal clause, which will be created as a
    :class:`_BindParamClause` with a bound value.

    :param value: the value to be bound. Can be any Python object supported by
        the underlying DB-API, or is translatable via the given type argument.

    :param type\_: an optional :class:`~sqlalchemy.types.TypeEngine` which
        will provide bind-parameter translation for this literal.

    """
    return _BindParamClause(None, value, type_=type_, unique=True)

def tuple_(*expr):
    """Return a SQL tuple.

    Main usage is to produce a composite IN construct::

        tuple_(table.c.col1, table.c.col2).in_(
            [(1, 2), (5, 12), (10, 19)]
        )

    .. warning::
    
        The composite IN construct is not supported by all backends, 
        and is currently known to work on Postgresql and MySQL,
        but not SQLite.   Unsupported backends will raise
        a subclass of :class:`~sqlalchemy.exc.DBAPIError` when such 
        an expression is invoked.

    """
    return _Tuple(*expr)

def type_coerce(expr, type_):
    """Coerce the given expression into the given type, on the Python side only.

    :func:`.type_coerce` is roughly similar to :func:`.cast`, except no
    "CAST" expression is rendered - the given type is only applied towards
    expression typing and against received result values.

    e.g.::

        from sqlalchemy.types import TypeDecorator
        import uuid

        class AsGuid(TypeDecorator):
            impl = String

            def process_bind_param(self, value, dialect):
                if value is not None:
                    return str(value)
                else:
                    return None

            def process_result_value(self, value, dialect):
                if value is not None:
                    return uuid.UUID(value)
                else:
                    return None

        conn.execute(
            select([type_coerce(mytable.c.ident, AsGuid)]).\\
                    where(
                        type_coerce(mytable.c.ident, AsGuid) == 
                        uuid.uuid3(uuid.NAMESPACE_URL, 'bar')
                    )
        )

    """
    if hasattr(expr, '__clause_expr__'):
        return type_coerce(expr.__clause_expr__())

    elif not isinstance(expr, Visitable):
        if expr is None:
            return null()
        else:
            return literal(expr, type_=type_)
    else:
        return _Label(None, expr, type_=type_)


def label(name, obj):
    """Return a :class:`_Label` object for the
    given :class:`.ColumnElement`.

    A label changes the name of an element in the columns clause of a
    ``SELECT`` statement, typically via the ``AS`` SQL keyword.

    This functionality is more conveniently available via the
    :func:`label()` method on :class:`.ColumnElement`.

    name
      label name

    obj
      a :class:`.ColumnElement`.

    """
    return _Label(name, obj)

def column(text, type_=None):
    """Return a textual column clause, as would be in the columns clause of a
    ``SELECT`` statement.

    The object returned is an instance of :class:`.ColumnClause`, which
    represents the "syntactical" portion of the schema-level
    :class:`~sqlalchemy.schema.Column` object.  It is often used directly
    within :func:`~.expression.select` constructs or with lightweight :func:`~.expression.table`
    constructs.

    Note that the :func:`~.expression.column` function is not part of
    the ``sqlalchemy`` namespace.  It must be imported from the ``sql`` package::

        from sqlalchemy.sql import table, column

    :param text: the name of the column.  Quoting rules will be applied 
      to the clause like any other column name. For textual column constructs
      that are not to be quoted, use the :func:`literal_column` function.

    :param type\_: an optional :class:`~sqlalchemy.types.TypeEngine` object 
      which will provide result-set translation for this column.

    See :class:`.ColumnClause` for further examples.

    """
    return ColumnClause(text, type_=type_)

def literal_column(text, type_=None):
    """Return a textual column expression, as would be in the columns
    clause of a ``SELECT`` statement.

    The object returned supports further expressions in the same way as any
    other column object, including comparison, math and string operations.
    The type\_ parameter is important to determine proper expression behavior
    (such as, '+' means string concatenation or numerical addition based on
    the type).

    :param text: the text of the expression; can be any SQL expression.
      Quoting rules will not be applied. To specify a column-name expression
      which should be subject to quoting rules, use the :func:`column`
      function.

    :param type\_: an optional :class:`~sqlalchemy.types.TypeEngine` object which will
      provide result-set translation and additional expression semantics for
      this column. If left as None the type will be NullType.

    """
    return ColumnClause(text, type_=type_, is_literal=True)

def table(name, *columns):
    """Represent a textual table clause.

    The object returned is an instance of :class:`.TableClause`, which represents the
    "syntactical" portion of the schema-level :class:`~.schema.Table` object. 
    It may be used to construct lightweight table constructs. 

    Note that the :func:`~.expression.table` function is not part of
    the ``sqlalchemy`` namespace.  It must be imported from the ``sql`` package::

        from sqlalchemy.sql import table, column

    :param name: Name of the table.

    :param columns: A collection of :func:`~.expression.column` constructs.

    See :class:`.TableClause` for further examples.

    """
    return TableClause(name, *columns)

def bindparam(key, value=None, type_=None, unique=False, required=False, callable_=None):
    """Create a bind parameter clause with the given key.

        :param key:
          the key for this bind param.  Will be used in the generated
          SQL statement for dialects that use named parameters.  This
          value may be modified when part of a compilation operation,
          if other :class:`_BindParamClause` objects exist with the same
          key, or if its length is too long and truncation is
          required.

        :param value:
          Initial value for this bind param.  This value may be
          overridden by the dictionary of parameters sent to statement
          compilation/execution.

        :param callable\_:
          A callable function that takes the place of "value".  The function
          will be called at statement execution time to determine the
          ultimate value.   Used for scenarios where the actual bind
          value cannot be determined at the point at which the clause
          construct is created, but embedded bind values are still desirable.

        :param type\_:
          A ``TypeEngine`` object that will be used to pre-process the
          value corresponding to this :class:`_BindParamClause` at
          execution time.

        :param unique:
          if True, the key name of this BindParamClause will be
          modified if another :class:`_BindParamClause` of the same name
          already has been located within the containing
          :class:`.ClauseElement`.

        :param required:
          a value is required at execution time.

    """
    if isinstance(key, ColumnClause):
        return _BindParamClause(key.name, value, type_=key.type, 
                                callable_=callable_,
                                unique=unique, required=required)
    else:
        return _BindParamClause(key, value, type_=type_, 
                                callable_=callable_,
                                unique=unique, required=required)

def outparam(key, type_=None):
    """Create an 'OUT' parameter for usage in functions (stored procedures),
    for databases which support them.

    The ``outparam`` can be used like a regular function parameter.
    The "output" value will be available from the
    :class:`~sqlalchemy.engine.ResultProxy` object via its ``out_parameters``
    attribute, which returns a dictionary containing the values.

    """
    return _BindParamClause(
                key, None, type_=type_, unique=False, isoutparam=True)

def text(text, bind=None, *args, **kwargs):
    """Create a SQL construct that is represented by a literal string.

    E.g.::

        t = text("SELECT * FROM users")
        result = connection.execute(t)

    The advantages :func:`text` provides over a plain string are
    backend-neutral support for bind parameters, per-statement
    execution options, as well as 
    bind parameter and result-column typing behavior, allowing 
    SQLAlchemy type constructs to play a role when executing
    a statement that is specified literally.

    Bind parameters are specified by name, using the format ``:name``.
    E.g.::

        t = text("SELECT * FROM users WHERE id=:user_id")
        result = connection.execute(t, user_id=12)

    To invoke SQLAlchemy typing logic for bind parameters, the 
    ``bindparams`` list allows specification of :func:`bindparam`
    constructs which specify the type for a given name::

        t = text("SELECT id FROM users WHERE updated_at>:updated",
                    bindparams=[bindparam('updated', DateTime())]
                )

    Typing during result row processing is also an important concern.
    Result column types
    are specified using the ``typemap`` dictionary, where the keys
    match the names of columns.  These names are taken from what
    the DBAPI returns as ``cursor.description``::

        t = text("SELECT id, name FROM users",
                typemap={
                    'id':Integer,
                    'name':Unicode
                }
        )

    The :func:`text` construct is used internally for most cases when
    a literal string is specified for part of a larger query, such as
    within :func:`select()`, :func:`update()`,
    :func:`insert()` or :func:`delete()`.   In those cases, the same
    bind parameter syntax is applied::

        s = select([users.c.id, users.c.name]).where("id=:user_id")
        result = connection.execute(s, user_id=12)

    Using :func:`text` explicitly usually implies the construction
    of a full, standalone statement.   As such, SQLAlchemy refers
    to it as an :class:`.Executable` object, and it supports
    the :meth:`Executable.execution_options` method.  For example,
    a :func:`text` construct that should be subject to "autocommit"
    can be set explicitly so using the ``autocommit`` option::

        t = text("EXEC my_procedural_thing()").\\
                execution_options(autocommit=True)

    Note that SQLAlchemy's usual "autocommit" behavior applies to
    :func:`text` constructs - that is, statements which begin
    with a phrase such as ``INSERT``, ``UPDATE``, ``DELETE``, 
    or a variety of other phrases specific to certain backends, will 
    be eligible for autocommit if no transaction is in progress.

    :param text:
      the text of the SQL statement to be created.  use ``:<param>``
      to specify bind parameters; they will be compiled to their
      engine-specific format.

    :param autocommit:
      Deprecated.  Use .execution_options(autocommit=<True|False>)
      to set the autocommit option.

    :param bind:
      an optional connection or engine to be used for this text query.

    :param bindparams:
      a list of :func:`bindparam()` instances which can be used to define
      the types and/or initial values for the bind parameters within
      the textual statement; the keynames of the bindparams must match
      those within the text of the statement.  The types will be used
      for pre-processing on bind values.

    :param typemap:
      a dictionary mapping the names of columns represented in the
      columns clause of a ``SELECT`` statement  to type objects,
      which will be used to perform post-processing on columns within
      the result set.   This argument applies to any expression 
      that returns result sets.

    """
    return _TextClause(text, bind=bind, *args, **kwargs)

def over(func, partition_by=None, order_by=None):
    """Produce an OVER clause against a function.

    Used against aggregate or so-called "window" functions,
    for database backends that support window functions.

    E.g.::

        from sqlalchemy import over
        over(func.row_number(), order_by='x')

    Would produce "ROW_NUMBER() OVER(ORDER BY x)".

    :param func: a :class:`.FunctionElement` construct, typically
     generated by :attr:`~.expression.func`.
    :param partition_by: a column element or string, or a list
     of such, that will be used as the PARTITION BY clause
     of the OVER construct.
    :param order_by: a column element or string, or a list
     of such, that will be used as the ORDER BY clause
     of the OVER construct.

    This function is also available from the :attr:`~.expression.func`
    construct itself via the :meth:`.FunctionElement.over` method.

    .. versionadded:: 0.7

    """
    return _Over(func, partition_by=partition_by, order_by=order_by)

def null():
    """Return a :class:`_Null` object, which compiles to ``NULL``.

    """
    return _Null()

def true():
    """Return a :class:`_True` object, which compiles to ``true``, or the 
    boolean equivalent for the target dialect.

    """
    return _True()

def false():
    """Return a :class:`_False` object, which compiles to ``false``, or the 
    boolean equivalent for the target dialect.

    """
    return _False()

class _FunctionGenerator(object):
    """Generate :class:`.Function` objects based on getattr calls."""

    def __init__(self, **opts):
        self.__names = []
        self.opts = opts

    def __getattr__(self, name):
        # passthru __ attributes; fixes pydoc
        if name.startswith('__'):
            try:
                return self.__dict__[name]
            except KeyError:
                raise AttributeError(name)

        elif name.endswith('_'):
            name = name[0:-1]
        f = _FunctionGenerator(**self.opts)
        f.__names = list(self.__names) + [name]
        return f

    def __call__(self, *c, **kwargs):
        o = self.opts.copy()
        o.update(kwargs)
        if len(self.__names) == 1:
            func = getattr(functions, self.__names[-1].lower(), None)
            if func is not None and \
                    isinstance(func, type) and \
                    issubclass(func, Function):
                return func(*c, **o)

        return Function(self.__names[-1],
                        packagenames=self.__names[0:-1], *c, **o)

# "func" global - i.e. func.count()
func = _FunctionGenerator()
"""Generate SQL function expressions.

   ``func`` is a special object instance which generates SQL functions based on name-based attributes, e.g.::

        >>> print func.count(1)
        count(:param_1)

   The element is a column-oriented SQL element like any other, and is
   used in that way::

        >>> print select([func.count(table.c.id)])
        SELECT count(sometable.id) FROM sometable

   Any name can be given to ``func``. If the function name is unknown to
   SQLAlchemy, it will be rendered exactly as is. For common SQL functions
   which SQLAlchemy is aware of, the name may be interpreted as a *generic
   function* which will be compiled appropriately to the target database::

        >>> print func.current_timestamp()
        CURRENT_TIMESTAMP

   To call functions which are present in dot-separated packages, specify them in the same manner::

        >>> print func.stats.yield_curve(5, 10)
        stats.yield_curve(:yield_curve_1, :yield_curve_2)

   SQLAlchemy can be made aware of the return type of functions to enable
   type-specific lexical and result-based behavior. For example, to ensure
   that a string-based function returns a Unicode value and is similarly
   treated as a string in expressions, specify
   :class:`~sqlalchemy.types.Unicode` as the type:

        >>> print func.my_string(u'hi', type_=Unicode) + ' ' + \
        ... func.my_string(u'there', type_=Unicode)
        my_string(:my_string_1) || :my_string_2 || my_string(:my_string_3)

   The object returned by a ``func`` call is an instance of :class:`.Function`.
   This object meets the "column" interface, including comparison and labeling
   functions.  The object can also be passed the :meth:`~.Connectable.execute`
   method of a :class:`.Connection` or :class:`.Engine`, where it will be
   wrapped inside of a SELECT statement first::

        print connection.execute(func.current_timestamp()).scalar()

   A function can also be "bound" to a :class:`.Engine` or :class:`.Connection`
   using the ``bind`` keyword argument, providing an execute() as well
   as a scalar() method::

        myfunc = func.current_timestamp(bind=some_engine)
        print myfunc.scalar()

   Functions which are interpreted as "generic" functions know how to
   calculate their return type automatically. For a listing of known generic
   functions, see :ref:`generic_functions`.

"""

# "modifier" global - i.e. modifier.distinct
# TODO: use UnaryExpression for this instead ?
modifier = _FunctionGenerator(group=False)

class _truncated_label(unicode):
    """A unicode subclass used to identify symbolic "
    "names that may require truncation."""

    def apply_map(self, map_):
        return self

# for backwards compatibility in case
# someone is re-implementing the 
# _truncated_identifier() sequence in a custom
# compiler
_generated_label = _truncated_label

class _anonymous_label(_truncated_label):
    """A unicode subclass used to identify anonymously 
    generated names."""

    def __add__(self, other):
        return _anonymous_label(
                    unicode(self) + 
                    unicode(other))

    def __radd__(self, other):
        return _anonymous_label(
                    unicode(other) + 
                    unicode(self))

    def apply_map(self, map_):
        return self % map_

def _as_truncated(value):
    """coerce the given value to :class:`._truncated_label`.
    
    Existing :class:`._truncated_label` and 
    :class:`._anonymous_label` objects are passed
    unchanged.
    """

    if isinstance(value, _truncated_label):
        return value
    else:
        return _truncated_label(value)

def _string_or_unprintable(element):
    if isinstance(element, basestring):
        return element
    else:
        try:
            return str(element)
        except:
            return "unprintable element %r" % element

def _clone(element, **kw):
    return element._clone()

def _expand_cloned(elements):
    """expand the given set of ClauseElements to be the set of all 'cloned'
    predecessors.

    """
    return itertools.chain(*[x._cloned_set for x in elements])

def _select_iterables(elements):
    """expand tables into individual columns in the 
    given list of column expressions.

    """
    return itertools.chain(*[c._select_iterable for c in elements])

def _cloned_intersection(a, b):
    """return the intersection of sets a and b, counting
    any overlap between 'cloned' predecessors.

    The returned set is in terms of the entities present within 'a'.

    """
    all_overlap = set(_expand_cloned(a)).intersection(_expand_cloned(b))
    return set(elem for elem in a
               if all_overlap.intersection(elem._cloned_set))


def _is_literal(element):
    return not isinstance(element, Visitable) and \
            not hasattr(element, '__clause_element__')

def _from_objects(*elements):
    return itertools.chain(*[element._from_objects for element in elements])

def _labeled(element):
    if not hasattr(element, 'name'):
        return element.label(None)
    else:
        return element

def _column_as_key(element):
    if isinstance(element, basestring):
        return element
    if hasattr(element, '__clause_element__'):
        element = element.__clause_element__()
    return element.key

def _literal_as_text(element):
    if isinstance(element, Visitable):
        return element
    elif hasattr(element, '__clause_element__'):
        return element.__clause_element__()
    elif isinstance(element, basestring):
        return _TextClause(unicode(element))
    elif isinstance(element, (util.NoneType, bool)):
        return _const_expr(element)
    else:
        raise exc.ArgumentError(
            "SQL expression object or string expected."
        )

def _const_expr(element):
    if element is None:
        return null()
    elif element is False:
        return false()
    elif element is True:
        return true()
    else:
        raise exc.ArgumentError(
            "Expected None, False, or True"
        )

def _clause_element_as_expr(element):
    if hasattr(element, '__clause_element__'):
        return element.__clause_element__()
    else:
        return element

def _literal_as_column(element):
    if isinstance(element, Visitable):
        return element
    elif hasattr(element, '__clause_element__'):
        return element.__clause_element__()
    else:
        return literal_column(str(element))

def _literal_as_binds(element, name=None, type_=None):
    if hasattr(element, '__clause_element__'):
        return element.__clause_element__()
    elif not isinstance(element, Visitable):
        if element is None:
            return null()
        else:
            return _BindParamClause(name, element, type_=type_, unique=True)
    else:
        return element

def _type_from_args(args):
    for a in args:
        if not isinstance(a.type, sqltypes.NullType):
            return a.type
    else:
        return sqltypes.NullType

def _no_literals(element):
    if hasattr(element, '__clause_element__'):
        return element.__clause_element__()
    elif not isinstance(element, Visitable):
        raise exc.ArgumentError("Ambiguous literal: %r.  Use the 'text()' "
                                "function to indicate a SQL expression "
                                "literal, or 'literal()' to indicate a "
                                "bound value." % element)
    else:
        return element

def _only_column_elements_or_none(element, name):
    if element is None:
        return None
    else:
        return _only_column_elements(element, name)

def _only_column_elements(element, name):
    if hasattr(element, '__clause_element__'):
        element = element.__clause_element__()
    if not isinstance(element, ColumnElement):
        raise exc.ArgumentError(
                "Column-based expression object expected for argument "
                "'%s'; got: '%s', type %s" % (name, element, type(element)))
    return element

def _corresponding_column_or_error(fromclause, column,
                                        require_embedded=False):
    c = fromclause.corresponding_column(column,
            require_embedded=require_embedded)
    if c is None:
        raise exc.InvalidRequestError(
                "Given column '%s', attached to table '%s', "
                "failed to locate a corresponding column from table '%s'"
                % 
                (column, 
                    getattr(column, 'table', None),fromclause.description)
                )
    return c

@util.decorator
def _generative(fn, *args, **kw):
    """Mark a method as generative."""

    self = args[0]._generate()
    fn(self, *args[1:], **kw)
    return self


def is_column(col):
    """True if ``col`` is an instance of :class:`.ColumnElement`."""

    return isinstance(col, ColumnElement)


class ClauseElement(Visitable):
    """Base class for elements of a programmatically constructed SQL
    expression.

    """
    __visit_name__ = 'clause'

    _annotations = {}
    supports_execution = False
    _from_objects = []
    bind = None
    _is_clone_of = None

    def _clone(self):
        """Create a shallow copy of this ClauseElement.

        This method may be used by a generative API.  Its also used as
        part of the "deep" copy afforded by a traversal that combines
        the _copy_internals() method.

        """
        c = self.__class__.__new__(self.__class__)
        c.__dict__ = self.__dict__.copy()
        c.__dict__.pop('_cloned_set', None)

        # this is a marker that helps to "equate" clauses to each other
        # when a Select returns its list of FROM clauses.  the cloning
        # process leaves around a lot of remnants of the previous clause
        # typically in the form of column expressions still attached to the
        # old table.
        c._is_clone_of = self

        return c

    @property
    def _constructor(self):
        """return the 'constructor' for this ClauseElement.

        This is for the purposes for creating a new object of 
        this type.   Usually, its just the element's __class__.
        However, the "Annotated" version of the object overrides
        to return the class of its proxied element.

        """
        return self.__class__

    @util.memoized_property
    def _cloned_set(self):
        """Return the set consisting all cloned ancestors of this
        ClauseElement.

        Includes this ClauseElement.  This accessor tends to be used for
        FromClause objects to identify 'equivalent' FROM clauses, regardless
        of transformative operations.

        """
        s = util.column_set()
        f = self
        while f is not None:
            s.add(f)
            f = f._is_clone_of
        return s

    def __getstate__(self):
        d = self.__dict__.copy()
        d.pop('_is_clone_of', None)
        return d

    if util.jython:
        def __hash__(self):
            """Return a distinct hash code.

            ClauseElements may have special equality comparisons which
            makes us rely on them having unique hash codes for use in
            hash-based collections. Stock __hash__ doesn't guarantee
            unique values on platforms with moving GCs.
            """
            return id(self)

    def _annotate(self, values):
        """return a copy of this ClauseElement with the given annotations
        dictionary.

        """
        return sqlutil.Annotated(self, values)

    def _deannotate(self):
        """return a copy of this ClauseElement with an empty annotations
        dictionary.

        """
        return self._clone()

    def unique_params(self, *optionaldict, **kwargs):
        """Return a copy with :func:`bindparam()` elements replaced.

        Same functionality as ``params()``, except adds `unique=True`
        to affected bind parameters so that multiple statements can be
        used.

        """
        return self._params(True, optionaldict, kwargs)

    def params(self, *optionaldict, **kwargs):
        """Return a copy with :func:`bindparam()` elements replaced.

        Returns a copy of this ClauseElement with :func:`bindparam()`
        elements replaced with values taken from the given dictionary::

          >>> clause = column('x') + bindparam('foo')
          >>> print clause.compile().params
          {'foo':None}
          >>> print clause.params({'foo':7}).compile().params
          {'foo':7}

        """
        return self._params(False, optionaldict, kwargs)

    def _params(self, unique, optionaldict, kwargs):
        if len(optionaldict) == 1:
            kwargs.update(optionaldict[0])
        elif len(optionaldict) > 1:
            raise exc.ArgumentError(
                "params() takes zero or one positional dictionary argument")

        def visit_bindparam(bind):
            if bind.key in kwargs:
                bind.value = kwargs[bind.key]
            if unique:
                bind._convert_to_unique()
        return cloned_traverse(self, {}, {'bindparam':visit_bindparam})

    def compare(self, other, **kw):
        """Compare this ClauseElement to the given ClauseElement.

        Subclasses should override the default behavior, which is a
        straight identity comparison.

        \**kw are arguments consumed by subclass compare() methods and
        may be used to modify the criteria for comparison.
        (see :class:`.ColumnElement`)

        """
        return self is other

    def _copy_internals(self, clone=_clone, **kw):
        """Reassign internal elements to be clones of themselves.

        Called during a copy-and-traverse operation on newly
        shallow-copied elements to create a deep copy.

        The given clone function should be used, which may be applying
        additional transformations to the element (i.e. replacement
        traversal, cloned traversal, annotations).

        """
        pass

    def get_children(self, **kwargs):
        """Return immediate child elements of this :class:`.ClauseElement`.

        This is used for visit traversal.

        \**kwargs may contain flags that change the collection that is
        returned, for example to return a subset of items in order to
        cut down on larger traversals, or to return child items from a
        different context (such as schema-level collections instead of
        clause-level).

        """
        return []

    def self_group(self, against=None):
        """Apply a 'grouping' to this :class:`.ClauseElement`.

        This method is overridden by subclasses to return a 
        "grouping" construct, i.e. parenthesis.   In particular
        it's used by "binary" expressions to provide a grouping
        around themselves when placed into a larger expression, 
        as well as by :func:`.select` constructs when placed into
        the FROM clause of another :func:`.select`.  (Note that 
        subqueries should be normally created using the 
        :func:`.Select.alias` method, as many platforms require
        nested SELECT statements to be named).

        As expressions are composed together, the application of
        :meth:`self_group` is automatic - end-user code should never 
        need to use this method directly.  Note that SQLAlchemy's
        clause constructs take operator precedence into account - 
        so parenthesis might not be needed, for example, in 
        an expression like ``x OR (y AND z)`` - AND takes precedence
        over OR.

        The base :meth:`self_group` method of :class:`.ClauseElement`
        just returns self.
        """
        return self


    @util.deprecated('0.7',
                              'Only SQL expressions which subclass '
                              ':class:`.Executable` may provide the '
                              ':func:`.execute` method.')
    def execute(self, *multiparams, **params):
        """Compile and execute this :class:`.ClauseElement`.

        """
        e = self.bind
        if e is None:
            label = getattr(self, 'description', self.__class__.__name__)
            msg = ('This %s does not support direct execution.' % label)
            raise exc.UnboundExecutionError(msg)
        return e._execute_clauseelement(self, multiparams, params)

    @util.deprecated('0.7',
                              'Only SQL expressions which subclass '
                              ':class:`.Executable` may provide the '
                              ':func:`.scalar` method.')
    def scalar(self, *multiparams, **params):
        """Compile and execute this :class:`.ClauseElement`, returning
        the result's scalar representation.

        """
        return self.execute(*multiparams, **params).scalar()

    def compile(self, bind=None, dialect=None, **kw):
        """Compile this SQL expression.

        The return value is a :class:`~sqlalchemy.engine.Compiled` object.
        Calling ``str()`` or ``unicode()`` on the returned value will yield a
        string representation of the result. The
        :class:`~sqlalchemy.engine.Compiled` object also can return a
        dictionary of bind parameter names and values
        using the ``params`` accessor.

        :param bind: An ``Engine`` or ``Connection`` from which a
            ``Compiled`` will be acquired. This argument takes precedence over
            this :class:`.ClauseElement`'s bound engine, if any.

        :param column_keys: Used for INSERT and UPDATE statements, a list of
            column names which should be present in the VALUES clause of the
            compiled statement. If ``None``, all columns from the target table
            object are rendered.

        :param dialect: A ``Dialect`` instance from which a ``Compiled``
            will be acquired. This argument takes precedence over the `bind`
            argument as well as this :class:`.ClauseElement`'s bound engine, if
            any.

        :param inline: Used for INSERT statements, for a dialect which does
            not support inline retrieval of newly generated primary key
            columns, will force the expression used to create the new primary
            key value to be rendered inline within the INSERT statement's
            VALUES clause. This typically refers to Sequence execution but may
            also refer to any server-side default generation function
            associated with a primary key `Column`.

        """

        if not dialect:
            if bind:
                dialect = bind.dialect
            elif self.bind:
                dialect = self.bind.dialect
                bind = self.bind
            else:
                dialect = default.DefaultDialect()
        return self._compiler(dialect, bind=bind, **kw)

    def _compiler(self, dialect, **kw):
        """Return a compiler appropriate for this ClauseElement, given a
        Dialect."""

        return dialect.statement_compiler(dialect, self, **kw)

    def __str__(self):
        # Py3K
        #return unicode(self.compile())
        # Py2K
        return unicode(self.compile()).encode('ascii', 'backslashreplace')
        # end Py2K

    def __and__(self, other):
        return and_(self, other)

    def __or__(self, other):
        return or_(self, other)

    def __invert__(self):
        return self._negate()

    def __nonzero__(self):
        raise TypeError("Boolean value of this clause is not defined")

    def _negate(self):
        if hasattr(self, 'negation_clause'):
            return self.negation_clause
        else:
            return _UnaryExpression(
                        self.self_group(against=operators.inv), 
                        operator=operators.inv, 
                        negate=None)

    def __repr__(self):
        friendly = getattr(self, 'description', None)
        if friendly is None:
            return object.__repr__(self)
        else:
            return '<%s.%s at 0x%x; %s>' % (
                self.__module__, self.__class__.__name__, id(self), friendly)


class _Immutable(object):
    """mark a ClauseElement as 'immutable' when expressions are cloned."""

    def unique_params(self, *optionaldict, **kwargs):
        raise NotImplementedError("Immutable objects do not support copying")

    def params(self, *optionaldict, **kwargs):
        raise NotImplementedError("Immutable objects do not support copying")

    def _clone(self):
        return self


class _CompareMixin(ColumnOperators):
    """Defines comparison and math operations for :class:`.ClauseElement`
    instances.

    See :class:`.ColumnOperators` and :class:`.Operators` for descriptions 
    of all operations.

    """

    def __compare(self, op, obj, negate=None, reverse=False,
                        **kwargs
        ):
        if obj is None or isinstance(obj, _Null):
            if op == operators.eq:
                return _BinaryExpression(self, null(), operators.is_,
                        negate=operators.isnot)
            elif op == operators.ne:
                return _BinaryExpression(self, null(), operators.isnot,
                        negate=operators.is_)
            else:
                raise exc.ArgumentError("Only '='/'!=' operators can "
                        "be used with NULL")
        else:
            obj = self._check_literal(op, obj)

        if reverse:
            return _BinaryExpression(obj, 
                            self, 
                            op, 
                            type_=sqltypes.BOOLEANTYPE, 
                            negate=negate, modifiers=kwargs)
        else:
            return _BinaryExpression(self, 
                            obj, 
                            op, 
                            type_=sqltypes.BOOLEANTYPE, 
                            negate=negate, modifiers=kwargs)

    def __operate(self, op, obj, reverse=False):
        obj = self._check_literal(op, obj)

        if reverse:
            left, right = obj, self
        else:
            left, right = self, obj

        if left.type is None:
            op, result_type = sqltypes.NULLTYPE._adapt_expression(op,
                    right.type)
        elif right.type is None:
            op, result_type = left.type._adapt_expression(op,
                    sqltypes.NULLTYPE)
        else:
            op, result_type = left.type._adapt_expression(op,
                    right.type)
        return _BinaryExpression(left, right, op, type_=result_type)


    # a mapping of operators with the method they use, along with their negated
    # operator for comparison operators
    operators = {
        operators.add : (__operate,),
        operators.mul : (__operate,),
        operators.sub : (__operate,),
        # Py2K
        operators.div : (__operate,),
        # end Py2K
        operators.mod : (__operate,),
        operators.truediv : (__operate,),
        operators.lt : (__compare, operators.ge),
        operators.le : (__compare, operators.gt),
        operators.ne : (__compare, operators.eq),
        operators.gt : (__compare, operators.le),
        operators.ge : (__compare, operators.lt),
        operators.eq : (__compare, operators.ne),
        operators.like_op : (__compare, operators.notlike_op),
        operators.ilike_op : (__compare, operators.notilike_op),
    }

    def operate(self, op, *other, **kwargs):
        o = _CompareMixin.operators[op]
        return o[0](self, op, other[0], *o[1:], **kwargs)

    def reverse_operate(self, op, other, **kwargs):
        o = _CompareMixin.operators[op]
        return o[0](self, op, other, reverse=True, *o[1:], **kwargs)

    def in_(self, other):
        """See :meth:`.ColumnOperators.in_`."""
        return self._in_impl(operators.in_op, operators.notin_op, other)

    def _in_impl(self, op, negate_op, seq_or_selectable):
        seq_or_selectable = _clause_element_as_expr(seq_or_selectable)

        if isinstance(seq_or_selectable, _ScalarSelect):
            return self.__compare(op, seq_or_selectable,
                                  negate=negate_op)
        elif isinstance(seq_or_selectable, _SelectBase):

            # TODO: if we ever want to support (x, y, z) IN (select x,
            # y, z from table), we would need a multi-column version of
            # as_scalar() to produce a multi- column selectable that
            # does not export itself as a FROM clause

            return self.__compare(op, seq_or_selectable.as_scalar(),
                                  negate=negate_op)
        elif isinstance(seq_or_selectable, (Selectable, _TextClause)):
            return self.__compare(op, seq_or_selectable,
                                  negate=negate_op)


        # Handle non selectable arguments as sequences

        args = []
        for o in seq_or_selectable:
            if not _is_literal(o):
                if not isinstance(o, _CompareMixin):
                    raise exc.InvalidRequestError('in() function accept'
                            's either a list of non-selectable values, '
                            'or a selectable: %r' % o)
            else:
                o = self._bind_param(op, o)
            args.append(o)
        if len(args) == 0:

            # Special case handling for empty IN's, behave like
            # comparison against zero row selectable.  We use != to
            # build the contradiction as it handles NULL values
            # appropriately, i.e. "not (x IN ())" should not return NULL
            # values for x.

            util.warn('The IN-predicate on "%s" was invoked with an '
                      'empty sequence. This results in a '
                      'contradiction, which nonetheless can be '
                      'expensive to evaluate.  Consider alternative '
                      'strategies for improved performance.' % self)
            return self != self

        return self.__compare(op,
                              ClauseList(*args).self_group(against=op),
                              negate=negate_op)

    def __neg__(self):
        """See :meth:`.ColumnOperators.__neg__`."""
        return _UnaryExpression(self, operator=operators.neg)

    def startswith(self, other, escape=None):
        """See :meth:`.ColumnOperators.startswith`."""
        # use __radd__ to force string concat behavior
        return self.__compare(
            operators.like_op,
            literal_column("'%'", type_=sqltypes.String).__radd__(
                                self._check_literal(operators.like_op, other)
                            ),
            escape=escape)

    def endswith(self, other, escape=None):
        """See :meth:`.ColumnOperators.endswith`."""
        return self.__compare(
            operators.like_op,
            literal_column("'%'", type_=sqltypes.String) + 
                self._check_literal(operators.like_op, other),
            escape=escape)

    def contains(self, other, escape=None):
        """See :meth:`.ColumnOperators.contains`."""
        return self.__compare(
            operators.like_op,
            literal_column("'%'", type_=sqltypes.String) +
                self._check_literal(operators.like_op, other) +
                literal_column("'%'", type_=sqltypes.String),
            escape=escape)

    def match(self, other):
        """See :meth:`.ColumnOperators.match`."""
        return self.__compare(operators.match_op,
                              self._check_literal(operators.match_op,
                              other))

    def label(self, name):
        """Produce a column label, i.e. ``<columnname> AS <name>``.

        This is a shortcut to the :func:`~.expression.label` function.

        if 'name' is None, an anonymous label name will be generated.

        """
        return _Label(name, self, self.type)

    def desc(self):
        """See :meth:`.ColumnOperators.desc`."""
        return desc(self)

    def asc(self):
        """See :meth:`.ColumnOperators.asc`."""
        return asc(self)

    def nullsfirst(self):
        """See :meth:`.ColumnOperators.nullsfirst`."""
        return nullsfirst(self)

    def nullslast(self):
        """See :meth:`.ColumnOperators.nullslast`."""
        return nullslast(self)

    def distinct(self):
        """See :meth:`.ColumnOperators.distinct`."""
        return _UnaryExpression(self, operator=operators.distinct_op,
                                type_=self.type)

    def between(self, cleft, cright):
        """See :meth:`.ColumnOperators.between`."""
        return _BinaryExpression(
                self,
                ClauseList(
                    self._check_literal(operators.and_, cleft),
                    self._check_literal(operators.and_, cright),
                    operator=operators.and_,
                    group=False),
                operators.between_op)

    def collate(self, collation):
        """See :meth:`.ColumnOperators.collate`."""

        return collate(self, collation)

    def op(self, operator):
        """See :meth:`.ColumnOperators.op`."""

        return lambda other: self.__operate(operator, other)

    def _bind_param(self, operator, obj):
        return _BindParamClause(None, obj, 
                                    _compared_to_operator=operator, 
                                    _compared_to_type=self.type, unique=True)

    def _check_literal(self, operator, other):
        if isinstance(other, _BindParamClause) and \
            isinstance(other.type, sqltypes.NullType):
            # TODO: perhaps we should not mutate the incoming bindparam()
            # here and instead make a copy of it.  this might
            # be the only place that we're mutating an incoming construct.
            other.type = self.type
            return other
        elif hasattr(other, '__clause_element__'):
            other = other.__clause_element__()
            if isinstance(other, (_SelectBase, Alias)):
                other = other.as_scalar()
            return other
        elif not isinstance(other, ClauseElement):
            return self._bind_param(operator, other)
        elif isinstance(other, (_SelectBase, Alias)):
            return other.as_scalar()
        else:
            return other


class ColumnElement(ClauseElement, _CompareMixin):
    """Represent an element that is usable within the "column clause" portion
    of a ``SELECT`` statement.

    This includes columns associated with tables, aliases, and
    subqueries, expressions, function calls, SQL keywords such as
    ``NULL``, literals, etc.  :class:`.ColumnElement` is the ultimate base
    class for all such elements.

    :class:`.ColumnElement` supports the ability to be a *proxy* element,
    which indicates that the :class:`.ColumnElement` may be associated with
    a :class:`.Selectable` which was derived from another :class:`.Selectable`.
    An example of a "derived" :class:`.Selectable` is an :class:`.Alias` of a
    :class:`~sqlalchemy.schema.Table`.

    A :class:`.ColumnElement`, by subclassing the :class:`_CompareMixin` mixin
    class, provides the ability to generate new :class:`.ClauseElement`
    objects using Python expressions.  See the :class:`_CompareMixin`
    docstring for more details.

    """

    __visit_name__ = 'column'
    primary_key = False
    foreign_keys = []
    quote = None
    _label = None
    _key_label = None
    _alt_names = ()

    @property
    def _select_iterable(self):
        return (self, )

    @util.memoized_property
    def base_columns(self):
        return util.column_set(c for c in self.proxy_set
                                     if not hasattr(c, 'proxies'))

    @util.memoized_property
    def proxy_set(self):
        s = util.column_set([self])
        if hasattr(self, 'proxies'):
            for c in self.proxies:
                s.update(c.proxy_set)
        return s

    def shares_lineage(self, othercolumn):
        """Return True if the given :class:`.ColumnElement` 
        has a common ancestor to this :class:`.ColumnElement`."""

        return bool(self.proxy_set.intersection(othercolumn.proxy_set))

    def _compare_name_for_result(self, other):
        """Return True if the given column element compares to this one
        when targeting within a result row."""

        return hasattr(other, 'name') and hasattr(self, 'name') and \
                other.name == self.name

    def _make_proxy(self, selectable, name=None):
        """Create a new :class:`.ColumnElement` representing this
        :class:`.ColumnElement` as it appears in the select list of a
        descending selectable.

        """
        if name is None:
            name = self.anon_label
            # TODO: may want to change this to anon_label,
            # or some value that is more useful than the
            # compiled form of the expression
            key = str(self)
        else:
            key = name

        co = ColumnClause(_as_truncated(name), 
                            selectable, 
                            type_=getattr(self,
                          'type', None))
        co.proxies = [self]
        if selectable._is_clone_of is not None:
            co._is_clone_of = \
                selectable._is_clone_of.columns.get(key)
        selectable._columns[key] = co
        return co

    def compare(self, other, use_proxies=False, equivalents=None, **kw):
        """Compare this ColumnElement to another.

        Special arguments understood:

        :param use_proxies: when True, consider two columns that
          share a common base column as equivalent (i.e. shares_lineage())

        :param equivalents: a dictionary of columns as keys mapped to sets
          of columns. If the given "other" column is present in this
          dictionary, if any of the columns in the corresponding set() pass the
          comparison test, the result is True. This is used to expand the
          comparison to other columns that may be known to be equivalent to
          this one via foreign key or other criterion.

        """
        to_compare = (other, )
        if equivalents and other in equivalents:
            to_compare = equivalents[other].union(to_compare)

        for oth in to_compare:
            if use_proxies and self.shares_lineage(oth):
                return True
            elif oth is self:
                return True
        else:
            return False

    @util.memoized_property
    def anon_label(self):
        """provides a constant 'anonymous label' for this ColumnElement.

        This is a label() expression which will be named at compile time.
        The same label() is returned each time anon_label is called so
        that expressions can reference anon_label multiple times, producing
        the same label name at compile time.

        the compiler uses this function automatically at compile time
        for expressions that are known to be 'unnamed' like binary
        expressions and function calls.

        """
        return _anonymous_label('%%(%d %s)s' % (id(self), getattr(self,
                                'name', 'anon')))

class ColumnCollection(util.OrderedProperties):
    """An ordered dictionary that stores a list of ColumnElement
    instances.

    Overrides the ``__eq__()`` method to produce SQL clauses between
    sets of correlated columns.

    """

    def __init__(self, *cols):
        super(ColumnCollection, self).__init__()
        self._data.update((c.key, c) for c in cols)
        self.__dict__['_all_cols'] = util.column_set(self)

    def __str__(self):
        return repr([str(c) for c in self])

    def replace(self, column):
        """add the given column to this collection, removing unaliased
           versions of this column  as well as existing columns with the
           same key.

            e.g.::

                t = Table('sometable', metadata, Column('col1', Integer))
                t.columns.replace(Column('col1', Integer, key='columnone'))

            will remove the original 'col1' from the collection, and add
            the new column under the name 'columnname'.

           Used by schema.Column to override columns during table reflection.

        """
        if column.name in self and column.key != column.name:
            other = self[column.name]
            if other.name == other.key:
                del self._data[other.name]
                self._all_cols.remove(other)
        if column.key in self._data:
            self._all_cols.remove(self._data[column.key])
        self._all_cols.add(column)
        self._data[column.key] = column

    def add(self, column):
        """Add a column to this collection.

        The key attribute of the column will be used as the hash key
        for this dictionary.

        """
        self[column.key] = column

    def __delitem__(self, key):
        raise NotImplementedError()

    def __setattr__(self, key, object):
        raise NotImplementedError()

    def __setitem__(self, key, value):
        if key in self:

            # this warning is primarily to catch select() statements
            # which have conflicting column names in their exported
            # columns collection

            existing = self[key]
            if not existing.shares_lineage(value):
                util.warn('Column %r on table %r being replaced by '
                          'another column with the same key.  Consider '
                          'use_labels for select() statements.' % (key,
                          getattr(existing, 'table', None)))
            self._all_cols.remove(existing)
            # pop out memoized proxy_set as this
            # operation may very well be occurring
            # in a _make_proxy operation
            value.__dict__.pop('proxy_set', None)
        self._all_cols.add(value)
        self._data[key] = value

    def clear(self):
        self._data.clear()
        self._all_cols.clear()

    def remove(self, column):
        del self._data[column.key]
        self._all_cols.remove(column)

    def update(self, value):
        self._data.update(value)
        self._all_cols.clear()
        self._all_cols.update(self._data.values())

    def extend(self, iter):
        self.update((c.key, c) for c in iter)

    __hash__ = None

    def __eq__(self, other):
        l = []
        for c in other:
            for local in self:
                if c.shares_lineage(local):
                    l.append(c==local)
        return and_(*l)

    def __contains__(self, other):
        if not isinstance(other, basestring):
            raise exc.ArgumentError("__contains__ requires a string argument")
        return util.OrderedProperties.__contains__(self, other)

    def __setstate__(self, state):
        self.__dict__['_data'] = state['_data']
        self.__dict__['_all_cols'] = util.column_set(self._data.values())

    def contains_column(self, col):
        # this has to be done via set() membership
        return col in self._all_cols

    def as_immutable(self):
        return ImmutableColumnCollection(self._data, self._all_cols)

class ImmutableColumnCollection(util.ImmutableProperties, ColumnCollection):
    def __init__(self, data, colset):
        util.ImmutableProperties.__init__(self, data)
        self.__dict__['_all_cols'] = colset

    extend = remove = util.ImmutableProperties._immutable


class ColumnSet(util.ordered_column_set):
    def contains_column(self, col):
        return col in self

    def extend(self, cols):
        for col in cols:
            self.add(col)

    def __add__(self, other):
        return list(self) + list(other)

    def __eq__(self, other):
        l = []
        for c in other:
            for local in self:
                if c.shares_lineage(local):
                    l.append(c==local)
        return and_(*l)

    def __hash__(self):
        return hash(tuple(x for x in self))

class Selectable(ClauseElement):
    """mark a class as being selectable"""
    __visit_name__ = 'selectable'

class FromClause(Selectable):
    """Represent an element that can be used within the ``FROM`` 
    clause of a ``SELECT`` statement.

    """
    __visit_name__ = 'fromclause'
    named_with_column = False
    _hide_froms = []
    quote = None
    schema = None
    _memoized_property = util.group_expirable_memoized_property(["_columns"]) 

    def count(self, whereclause=None, **params):
        """return a SELECT COUNT generated against this
        :class:`.FromClause`."""

        if self.primary_key:
            col = list(self.primary_key)[0]
        else:
            col = list(self.columns)[0]
        return select(
                    [func.count(col).label('tbl_row_count')], 
                    whereclause, 
                    from_obj=[self], 
                    **params)

    def select(self, whereclause=None, **params):
        """return a SELECT of this :class:`.FromClause`."""

        return select([self], whereclause, **params)

    def join(self, right, onclause=None, isouter=False):
        """return a join of this :class:`.FromClause` against another
        :class:`.FromClause`."""

        return Join(self, right, onclause, isouter)

    def outerjoin(self, right, onclause=None):
        """return an outer join of this :class:`.FromClause` against another
        :class:`.FromClause`."""

        return Join(self, right, onclause, True)

    def alias(self, name=None):
        """return an alias of this :class:`.FromClause`.

        This is shorthand for calling::

            from sqlalchemy import alias
            a = alias(self, name=name)

        See :func:`~.expression.alias` for details.

        """

        return Alias(self, name)

    def is_derived_from(self, fromclause):
        """Return True if this FromClause is 'derived' from the given
        FromClause.

        An example would be an Alias of a Table is derived from that Table.

        """
        return fromclause in self._cloned_set

    def replace_selectable(self, old, alias):
        """replace all occurrences of FromClause 'old' with the given Alias 
        object, returning a copy of this :class:`.FromClause`.

        """

        return sqlutil.ClauseAdapter(alias).traverse(self)

    def correspond_on_equivalents(self, column, equivalents):
        """Return corresponding_column for the given column, or if None
        search for a match in the given dictionary.

        """
        col = self.corresponding_column(column, require_embedded=True)
        if col is None and col in equivalents:
            for equiv in equivalents[col]:
                nc = self.corresponding_column(equiv, require_embedded=True)
                if nc:
                    return nc
        return col

    def corresponding_column(self, column, require_embedded=False):
        """Given a :class:`.ColumnElement`, return the exported
        :class:`.ColumnElement` object from this :class:`.Selectable`
        which corresponds to that original
        :class:`~sqlalchemy.schema.Column` via a common ancestor
        column.

        :param column: the target :class:`.ColumnElement` to be matched

        :param require_embedded: only return corresponding columns for
        the given :class:`.ColumnElement`, if the given
        :class:`.ColumnElement` is actually present within a sub-element
        of this :class:`.FromClause`.  Normally the column will match if
        it merely shares a common ancestor with one of the exported
        columns of this :class:`.FromClause`.

        """

        def embedded(expanded_proxy_set, target_set):
            for t in target_set.difference(expanded_proxy_set):
                if not set(_expand_cloned([t])
                            ).intersection(expanded_proxy_set):
                    return False
            return True

        # don't dig around if the column is locally present
        if self.c.contains_column(column):
            return column
        col, intersect = None, None
        target_set = column.proxy_set
        cols = self.c
        for c in cols:
            expanded_proxy_set = set(_expand_cloned(c.proxy_set))
            i = target_set.intersection(expanded_proxy_set)
            if i and (not require_embedded
                      or embedded(expanded_proxy_set, target_set)):
                if col is None:

                    # no corresponding column yet, pick this one.

                    col, intersect = c, i
                elif len(i) > len(intersect):

                    # 'c' has a larger field of correspondence than
                    # 'col'. i.e. selectable.c.a1_x->a1.c.x->table.c.x
                    # matches a1.c.x->table.c.x better than
                    # selectable.c.x->table.c.x does.

                    col, intersect = c, i
                elif i == intersect:

                    # they have the same field of correspondence. see
                    # which proxy_set has fewer columns in it, which
                    # indicates a closer relationship with the root
                    # column. Also take into account the "weight"
                    # attribute which CompoundSelect() uses to give
                    # higher precedence to columns based on vertical
                    # position in the compound statement, and discard
                    # columns that have no reference to the target
                    # column (also occurs with CompoundSelect)

                    col_distance = util.reduce(operator.add,
                            [sc._annotations.get('weight', 1) for sc in
                            col.proxy_set if sc.shares_lineage(column)])
                    c_distance = util.reduce(operator.add,
                            [sc._annotations.get('weight', 1) for sc in
                            c.proxy_set if sc.shares_lineage(column)])
                    if c_distance < col_distance:
                        col, intersect = c, i
        return col

    @property
    def description(self):
        """a brief description of this FromClause.

        Used primarily for error message formatting.

        """
        return getattr(self, 'name', self.__class__.__name__ + " object")

    def _reset_exported(self):
        """delete memoized collections when a FromClause is cloned."""

        self._memoized_property.expire_instance(self)

    @_memoized_property
    def columns(self):
        """Return the collection of Column objects contained by this
        FromClause."""

        if '_columns' not in self.__dict__:
            self._init_collections()
            self._populate_column_collection()
        return self._columns.as_immutable()

    @_memoized_property
    def primary_key(self):
        """Return the collection of Column objects which comprise the
        primary key of this FromClause."""

        self._init_collections()
        self._populate_column_collection()
        return self.primary_key

    @_memoized_property
    def foreign_keys(self):
        """Return the collection of ForeignKey objects which this
        FromClause references."""

        self._init_collections()
        self._populate_column_collection()
        return self.foreign_keys

    c = property(attrgetter('columns'))
    _select_iterable = property(attrgetter('columns'))

    def _init_collections(self):
        assert '_columns' not in self.__dict__
        assert 'primary_key' not in self.__dict__
        assert 'foreign_keys' not in self.__dict__

        self._columns = ColumnCollection()
        self.primary_key = ColumnSet()
        self.foreign_keys = set()

    def _populate_column_collection(self):
        pass

class _BindParamClause(ColumnElement):
    """Represent a bind parameter.

    Public constructor is the :func:`bindparam()` function.

    """

    __visit_name__ = 'bindparam'
    quote = None

    def __init__(self, key, value, type_=None, unique=False, 
                            callable_=None,
                            isoutparam=False, required=False, 
                            _compared_to_operator=None,
                            _compared_to_type=None):
        """Construct a _BindParamClause.

        :param key:
          the key for this bind param.  Will be used in the generated
          SQL statement for dialects that use named parameters.  This
          value may be modified when part of a compilation operation,
          if other :class:`_BindParamClause` objects exist with the same
          key, or if its length is too long and truncation is
          required.

        :param value:
          Initial value for this bind param.  This value may be
          overridden by the dictionary of parameters sent to statement
          compilation/execution.

        :param callable\_:
          A callable function that takes the place of "value".  The function
          will be called at statement execution time to determine the
          ultimate value.   Used for scenarios where the actual bind
          value cannot be determined at the point at which the clause
          construct is created, but embedded bind values are still desirable.

        :param type\_:
          A ``TypeEngine`` object that will be used to pre-process the
          value corresponding to this :class:`_BindParamClause` at
          execution time.

        :param unique:
          if True, the key name of this BindParamClause will be
          modified if another :class:`_BindParamClause` of the same name
          already has been located within the containing
          :class:`.ClauseElement`.

        :param required:
          a value is required at execution time.

        :param isoutparam:
          if True, the parameter should be treated like a stored procedure
          "OUT" parameter.

        """
        if unique:
            self.key = _anonymous_label('%%(%d %s)s' % (id(self), key
                    or 'param'))
        else:
            self.key = key or _anonymous_label('%%(%d param)s'
                    % id(self))

        # identifying key that won't change across
        # clones, used to identify the bind's logical
        # identity
        self._identifying_key = self.key

        # key that was passed in the first place, used to 
        # generate new keys
        self._orig_key = key or 'param'

        self.unique = unique
        self.value = value
        self.callable = callable_
        self.isoutparam = isoutparam
        self.required = required
        if type_ is None:
            if _compared_to_type is not None:
                self.type = \
                    _compared_to_type._coerce_compared_value(
                        _compared_to_operator, value)
            else:
                self.type = sqltypes._type_map.get(type(value),
                        sqltypes.NULLTYPE)
        elif isinstance(type_, type):
            self.type = type_()
        else:
            self.type = type_

    @property
    def effective_value(self):
        """Return the value of this bound parameter, 
        taking into account if the ``callable`` parameter
        was set.  
        
        The ``callable`` value will be evaluated
        and returned if present, else ``value``.
        
        """
        if self.callable:
            return self.callable()
        else:
            return self.value

    def _clone(self):
        c = ClauseElement._clone(self)
        if self.unique:
            c.key = _anonymous_label('%%(%d %s)s' % (id(c), c._orig_key
                    or 'param'))
        return c

    def _convert_to_unique(self):
        if not self.unique:
            self.unique = True
            self.key = _anonymous_label('%%(%d %s)s' % (id(self),
                    self._orig_key or 'param'))

    def compare(self, other, **kw):
        """Compare this :class:`_BindParamClause` to the given
        clause."""

        return isinstance(other, _BindParamClause) \
            and self.type._compare_type_affinity(other.type) \
            and self.value == other.value

    def __getstate__(self):
        """execute a deferred value for serialization purposes."""

        d = self.__dict__.copy()
        v = self.value
        if self.callable:
            v = self.callable()
            d['callable'] = None
        d['value'] = v
        return d

    def __repr__(self):
        return '_BindParamClause(%r, %r, type_=%r)' % (self.key,
                self.value, self.type)

class _TypeClause(ClauseElement):
    """Handle a type keyword in a SQL statement.

    Used by the ``Case`` statement.

    """

    __visit_name__ = 'typeclause'

    def __init__(self, type):
        self.type = type


class _Generative(object):
    """Allow a ClauseElement to generate itself via the
    @_generative decorator.

    """

    def _generate(self):
        s = self.__class__.__new__(self.__class__)
        s.__dict__ = self.__dict__.copy()
        return s


class Executable(_Generative):
    """Mark a ClauseElement as supporting execution.

    :class:`.Executable` is a superclass for all "statement" types
    of objects, including :func:`select`, :func:`delete`, :func:`update`,
    :func:`insert`, :func:`text`.

    """

    supports_execution = True
    _execution_options = util.immutabledict()
    _bind = None

    @_generative
    def execution_options(self, **kw):
        """ Set non-SQL options for the statement which take effect during
        execution.

        Execution options can be set on a per-statement or 
        per :class:`.Connection` basis.   Additionally, the 
        :class:`.Engine` and ORM :class:`~.orm.query.Query` objects provide access
        to execution options which they in turn configure upon connections.

        The :meth:`execution_options` method is generative.  A new 
        instance of this statement is returned that contains the options::

            statement = select([table.c.x, table.c.y])
            statement = statement.execution_options(autocommit=True)

        Note that only a subset of possible execution options can be applied
        to a statement - these include "autocommit" and "stream_results",
        but not "isolation_level" or "compiled_cache".
        See :meth:`.Connection.execution_options` for a full list of 
        possible options.

        See also:

            :meth:`.Connection.execution_options()`

            :meth:`.Query.execution_options()`

        """
        if 'isolation_level' in kw:
            raise exc.ArgumentError(
                "'isolation_level' execution option may only be specified "
                "on Connection.execution_options(), or "
                "per-engine using the isolation_level "
                "argument to create_engine()."
            )
        if 'compiled_cache' in kw:
            raise exc.ArgumentError(
                "'compiled_cache' execution option may only be specified "
                "on Connection.execution_options(), not per statement."
            )
        self._execution_options = self._execution_options.union(kw)

    def execute(self, *multiparams, **params):
        """Compile and execute this :class:`.Executable`."""

        e = self.bind
        if e is None:
            label = getattr(self, 'description', self.__class__.__name__)
            msg = ('This %s is not directly bound to a Connection or Engine.'
                   'Use the .execute() method of a Connection or Engine '
                   'to execute this construct.' % label)
            raise exc.UnboundExecutionError(msg)
        return e._execute_clauseelement(self, multiparams, params)

    def scalar(self, *multiparams, **params):
        """Compile and execute this :class:`.Executable`, returning the
        result's scalar representation.

        """
        return self.execute(*multiparams, **params).scalar()

    @property
    def bind(self):
        """Returns the :class:`.Engine` or :class:`.Connection` to 
        which this :class:`.Executable` is bound, or None if none found.

        This is a traversal which checks locally, then
        checks among the "from" clauses of associated objects
        until a bound engine or connection is found.

        """
        if self._bind is not None:
            return self._bind

        for f in _from_objects(self):
            if f is self:
                continue
            engine = f.bind
            if engine is not None:
                return engine
        else:
            return None


# legacy, some outside users may be calling this
_Executable = Executable

class _TextClause(Executable, ClauseElement):
    """Represent a literal SQL text fragment.

    Public constructor is the :func:`text()` function.

    """

    __visit_name__ = 'textclause'

    _bind_params_regex = re.compile(r'(?<![:\w\x5c]):(\w+)(?!:)', re.UNICODE)
    _execution_options = \
        Executable._execution_options.union({'autocommit'
            : PARSE_AUTOCOMMIT})

    @property
    def _select_iterable(self):
        return (self,)

    _hide_froms = []

    def __init__(
        self,
        text='',
        bind=None,
        bindparams=None,
        typemap=None,
        autocommit=None,
        ):
        self._bind = bind
        self.bindparams = {}
        self.typemap = typemap
        if autocommit is not None:
            util.warn_deprecated('autocommit on text() is deprecated.  '
                                 'Use .execution_options(autocommit=Tru'
                                 'e)')
            self._execution_options = \
                self._execution_options.union({'autocommit'
                    : autocommit})
        if typemap is not None:
            for key in typemap.keys():
                typemap[key] = sqltypes.to_instance(typemap[key])

        def repl(m):
            self.bindparams[m.group(1)] = bindparam(m.group(1))
            return ':%s' % m.group(1)

        # scan the string and search for bind parameter names, add them
        # to the list of bindparams

        self.text = self._bind_params_regex.sub(repl, text)
        if bindparams is not None:
            for b in bindparams:
                self.bindparams[b.key] = b

    @property
    def type(self):
        if self.typemap is not None and len(self.typemap) == 1:
            return list(self.typemap)[0]
        else:
            return sqltypes.NULLTYPE

    def self_group(self, against=None):
        if against is operators.in_op:
            return _Grouping(self)
        else:
            return self

    def _copy_internals(self, clone=_clone, **kw):
        self.bindparams = dict((b.key, clone(b, **kw))
                               for b in self.bindparams.values())

    def get_children(self, **kwargs):
        return self.bindparams.values()


class _Null(ColumnElement):
    """Represent the NULL keyword in a SQL statement.

    Public constructor is the :func:`null()` function.

    """

    __visit_name__ = 'null'
    def __init__(self):
        self.type = sqltypes.NULLTYPE

class _False(ColumnElement):
    """Represent the ``false`` keyword in a SQL statement.

    Public constructor is the :func:`false()` function.

    """

    __visit_name__ = 'false'
    def __init__(self):
        self.type = sqltypes.BOOLEANTYPE

class _True(ColumnElement):
    """Represent the ``true`` keyword in a SQL statement.

    Public constructor is the :func:`true()` function.

    """

    __visit_name__ = 'true'
    def __init__(self):
        self.type = sqltypes.BOOLEANTYPE


class ClauseList(ClauseElement):
    """Describe a list of clauses, separated by an operator.

    By default, is comma-separated, such as a column listing.

    """
    __visit_name__ = 'clauselist'

    def __init__(self, *clauses, **kwargs):
        self.operator = kwargs.pop('operator', operators.comma_op)
        self.group = kwargs.pop('group', True)
        self.group_contents = kwargs.pop('group_contents', True)
        if self.group_contents:
            self.clauses = [
                _literal_as_text(clause).self_group(against=self.operator)
                for clause in clauses if clause is not None]
        else:
            self.clauses = [
                _literal_as_text(clause)
                for clause in clauses if clause is not None]

    @util.memoized_property
    def type(self):
        if self.clauses:
            return self.clauses[0].type
        else:
            return sqltypes.NULLTYPE

    def __iter__(self):
        return iter(self.clauses)

    def __len__(self):
        return len(self.clauses)

    @property
    def _select_iterable(self):
        return iter(self)

    def append(self, clause):
        # TODO: not sure if i like the 'group_contents' flag.  need to
        # define the difference between a ClauseList of ClauseLists,
        # and a "flattened" ClauseList of ClauseLists.  flatten()
        # method ?
        if self.group_contents:
            self.clauses.append(_literal_as_text(clause).\
                                self_group(against=self.operator))
        else:
            self.clauses.append(_literal_as_text(clause))

    def _copy_internals(self, clone=_clone, **kw):
        self.clauses = [clone(clause, **kw) for clause in self.clauses]

    def get_children(self, **kwargs):
        return self.clauses

    @property
    def _from_objects(self):
        return list(itertools.chain(*[c._from_objects for c in self.clauses]))

    def self_group(self, against=None):
        if self.group and operators.is_precedent(self.operator, against):
            return _Grouping(self)
        else:
            return self

    def compare(self, other, **kw):
        """Compare this :class:`.ClauseList` to the given :class:`.ClauseList`,
        including a comparison of all the clause items.

        """
        if not isinstance(other, ClauseList) and len(self.clauses) == 1:
            return self.clauses[0].compare(other, **kw)
        elif isinstance(other, ClauseList) and \
                len(self.clauses) == len(other.clauses):
            for i in range(0, len(self.clauses)):
                if not self.clauses[i].compare(other.clauses[i], **kw):
                    return False
            else:
                return self.operator == other.operator
        else:
            return False

class BooleanClauseList(ClauseList, ColumnElement):
    __visit_name__ = 'clauselist'

    def __init__(self, *clauses, **kwargs):
        super(BooleanClauseList, self).__init__(*clauses, **kwargs)
        self.type = sqltypes.to_instance(kwargs.get('type_',
                sqltypes.Boolean))

    @property
    def _select_iterable(self):
        return (self, )

    def self_group(self, against=None):
        if not self.clauses:
            return self
        else:
            return super(BooleanClauseList, self).self_group(against=against)

class _Tuple(ClauseList, ColumnElement):

    def __init__(self, *clauses, **kw):
        clauses = [_literal_as_binds(c) for c in clauses]
        super(_Tuple, self).__init__(*clauses, **kw)
        self.type = _type_from_args(clauses)

    @property
    def _select_iterable(self):
        return (self, )

    def _bind_param(self, operator, obj):
        return _Tuple(*[
            _BindParamClause(None, o, _compared_to_operator=operator,
                             _compared_to_type=self.type, unique=True)
            for o in obj
        ]).self_group()


class _Case(ColumnElement):
    __visit_name__ = 'case'

    def __init__(self, whens, value=None, else_=None):
        try:
            whens = util.dictlike_iteritems(whens)
        except TypeError:
            pass

        if value is not None:
            whenlist = [
                (_literal_as_binds(c).self_group(), 
                _literal_as_binds(r)) for (c, r) in whens
            ]
        else:
            whenlist = [
                (_no_literals(c).self_group(), 
                _literal_as_binds(r)) for (c, r) in whens
            ]

        if whenlist:
            type_ = list(whenlist[-1])[-1].type
        else:
            type_ = None

        if value is None:
            self.value = None
        else:
            self.value = _literal_as_binds(value)

        self.type = type_
        self.whens = whenlist
        if else_ is not None:
            self.else_ = _literal_as_binds(else_)
        else:
            self.else_ = None

    def _copy_internals(self, clone=_clone, **kw):
        if self.value is not None:
            self.value = clone(self.value, **kw)
        self.whens = [(clone(x, **kw), clone(y, **kw)) 
                            for x, y in self.whens]
        if self.else_ is not None:
            self.else_ = clone(self.else_, **kw)

    def get_children(self, **kwargs):
        if self.value is not None:
            yield self.value
        for x, y in self.whens:
            yield x
            yield y
        if self.else_ is not None:
            yield self.else_ 

    @property
    def _from_objects(self):
        return list(itertools.chain(*[x._from_objects for x in
                    self.get_children()]))

class FunctionElement(Executable, ColumnElement, FromClause):
    """Base for SQL function-oriented constructs."""

    packagenames = ()

    def __init__(self, *clauses, **kwargs):
        """Construct a :class:`.FunctionElement`.
        """
        args = [_literal_as_binds(c, self.name) for c in clauses]
        self.clause_expr = ClauseList(
                                operator=operators.comma_op,
                                 group_contents=True, *args).\
                                 self_group()

    @property
    def columns(self):
        """Fulfill the 'columns' contract of :class:`.ColumnElement`.

        Returns a single-element list consisting of this object.

        """
        return [self]

    @util.memoized_property
    def clauses(self):
        """Return the underlying :class:`.ClauseList` which contains
        the arguments for this :class:`.FunctionElement`.

        """
        return self.clause_expr.element

    def over(self, partition_by=None, order_by=None):
        """Produce an OVER clause against this function.

        Used against aggregate or so-called "window" functions,
        for database backends that support window functions.

        The expression::

            func.row_number().over(order_by='x')

        is shorthand for::

            from sqlalchemy import over
            over(func.row_number(), order_by='x')

        See :func:`~.expression.over` for a full description.

        .. versionadded:: 0.7

        """
        return over(self, partition_by=partition_by, order_by=order_by)

    @property
    def _from_objects(self):
        return self.clauses._from_objects

    def get_children(self, **kwargs):
        return self.clause_expr, 

    def _copy_internals(self, clone=_clone, **kw):
        self.clause_expr = clone(self.clause_expr, **kw)
        self._reset_exported()
        util.reset_memoized(self, 'clauses')

    def select(self):
        """Produce a :func:`~.expression.select` construct 
        against this :class:`.FunctionElement`.

        This is shorthand for::

            s = select([function_element])

        """
        s = select([self])
        if self._execution_options:
            s = s.execution_options(**self._execution_options)
        return s

    def scalar(self):
        """Execute this :class:`.FunctionElement` against an embedded
        'bind' and return a scalar value.

        This first calls :meth:`~.FunctionElement.select` to 
        produce a SELECT construct.

        Note that :class:`.FunctionElement` can be passed to 
        the :meth:`.Connectable.scalar` method of :class:`.Connection`
        or :class:`.Engine`.

        """
        return self.select().execute().scalar()

    def execute(self):
        """Execute this :class:`.FunctionElement` against an embedded
        'bind'.

        This first calls :meth:`~.FunctionElement.select` to 
        produce a SELECT construct.

        Note that :class:`.FunctionElement` can be passed to 
        the :meth:`.Connectable.execute` method of :class:`.Connection`
        or :class:`.Engine`.

        """
        return self.select().execute()

    def _bind_param(self, operator, obj):
        return _BindParamClause(None, obj, _compared_to_operator=operator, 
                                _compared_to_type=self.type, unique=True)


class Function(FunctionElement):
    """Describe a named SQL function.

    See the superclass :class:`.FunctionElement` for a description
    of public methods.

    """

    __visit_name__ = 'function'

    def __init__(self, name, *clauses, **kw):
        """Construct a :class:`.Function`.

        The :attr:`.func` construct is normally used to construct 
        new :class:`.Function` instances.

        """
        self.packagenames = kw.pop('packagenames', None) or []
        self.name = name
        self._bind = kw.get('bind', None)
        self.type = sqltypes.to_instance(kw.get('type_', None))

        FunctionElement.__init__(self, *clauses, **kw)

    def _bind_param(self, operator, obj):
        return _BindParamClause(self.name, obj,
                                _compared_to_operator=operator,
                                _compared_to_type=self.type,
                                unique=True)


class _Cast(ColumnElement):

    __visit_name__ = 'cast'

    def __init__(self, clause, totype, **kwargs):
        self.type = sqltypes.to_instance(totype)
        self.clause = _literal_as_binds(clause, None)
        self.typeclause = _TypeClause(self.type)

    def _copy_internals(self, clone=_clone, **kw):
        self.clause = clone(self.clause, **kw)
        self.typeclause = clone(self.typeclause, **kw)

    def get_children(self, **kwargs):
        return self.clause, self.typeclause

    @property
    def _from_objects(self):
        return self.clause._from_objects


class _Extract(ColumnElement):

    __visit_name__ = 'extract'

    def __init__(self, field, expr, **kwargs):
        self.type = sqltypes.Integer()
        self.field = field
        self.expr = _literal_as_binds(expr, None)

    def _copy_internals(self, clone=_clone, **kw):
        self.expr = clone(self.expr, **kw)

    def get_children(self, **kwargs):
        return self.expr,

    @property
    def _from_objects(self):
        return self.expr._from_objects


class _UnaryExpression(ColumnElement):

    __visit_name__ = 'unary'

    def __init__(self, element, operator=None, modifier=None, 
                            type_=None, negate=None):
        self.operator = operator
        self.modifier = modifier

        self.element = _literal_as_text(element).\
                    self_group(against=self.operator or self.modifier)
        self.type = sqltypes.to_instance(type_)
        self.negate = negate

    @property
    def _from_objects(self):
        return self.element._from_objects

    def _copy_internals(self, clone=_clone, **kw):
        self.element = clone(self.element, **kw)

    def get_children(self, **kwargs):
        return self.element,

    def compare(self, other, **kw):
        """Compare this :class:`_UnaryExpression` against the given
        :class:`.ClauseElement`."""

        return (
            isinstance(other, _UnaryExpression) and
            self.operator == other.operator and
            self.modifier == other.modifier and
            self.element.compare(other.element, **kw)
        )

    def _negate(self):
        if self.negate is not None:
            return _UnaryExpression(
                self.element,
                operator=self.negate,
                negate=self.operator,
                modifier=self.modifier,
                type_=self.type)
        else:
            return super(_UnaryExpression, self)._negate()

    def self_group(self, against=None):
        if self.operator and operators.is_precedent(self.operator,
                against):
            return _Grouping(self)
        else:
            return self


class _BinaryExpression(ColumnElement):
    """Represent an expression that is ``LEFT <operator> RIGHT``."""

    __visit_name__ = 'binary'

    def __init__(self, left, right, operator, type_=None, 
                    negate=None, modifiers=None):
        self.left = _literal_as_text(left).self_group(against=operator)
        self.right = _literal_as_text(right).self_group(against=operator)
        self.operator = operator
        self.type = sqltypes.to_instance(type_)
        self.negate = negate
        if modifiers is None:
            self.modifiers = {}
        else:
            self.modifiers = modifiers

    def __nonzero__(self):
        try:
            return self.operator(hash(self.left), hash(self.right))
        except:
            raise TypeError("Boolean value of this clause is not defined")

    @property
    def _from_objects(self):
        return self.left._from_objects + self.right._from_objects

    def _copy_internals(self, clone=_clone, **kw):
        self.left = clone(self.left, **kw)
        self.right = clone(self.right, **kw)

    def get_children(self, **kwargs):
        return self.left, self.right

    def compare(self, other, **kw):
        """Compare this :class:`_BinaryExpression` against the 
        given :class:`_BinaryExpression`."""

        return (
            isinstance(other, _BinaryExpression) and
            self.operator == other.operator and
            (
                self.left.compare(other.left, **kw) and
                self.right.compare(other.right, **kw) or
                (
                    operators.is_commutative(self.operator) and
                    self.left.compare(other.right, **kw) and
                    self.right.compare(other.left, **kw)
                )
            )
        )

    def self_group(self, against=None):
        if operators.is_precedent(self.operator, against):
            return _Grouping(self)
        else:
            return self

    def _negate(self):
        if self.negate is not None:
            return _BinaryExpression(
                self.left,
                self.right,
                self.negate,
                negate=self.operator,
                type_=sqltypes.BOOLEANTYPE,
                modifiers=self.modifiers)
        else:
            return super(_BinaryExpression, self)._negate()

class _Exists(_UnaryExpression):
    __visit_name__ = _UnaryExpression.__visit_name__
    _from_objects = []

    def __init__(self, *args, **kwargs):
        if args and isinstance(args[0], (_SelectBase, _ScalarSelect)):
            s = args[0]
        else:
            if not args:
                args = ([literal_column('*')],)
            s = select(*args, **kwargs).as_scalar().self_group()

        _UnaryExpression.__init__(self, s, operator=operators.exists,
                                  type_=sqltypes.Boolean)

    def select(self, whereclause=None, **params):
        return select([self], whereclause, **params)

    def correlate(self, fromclause):
        e = self._clone()
        e.element = self.element.correlate(fromclause).self_group()
        return e

    def select_from(self, clause):
        """return a new :class:`._Exists` construct, applying the given expression
        to the :meth:`.Select.select_from` method of the select statement
        contained.

        """
        e = self._clone()
        e.element = self.element.select_from(clause).self_group()
        return e

    def where(self, clause):
        """return a new exists() construct with the given expression added to
        its WHERE clause, joined to the existing clause via AND, if any.

        """
        e = self._clone()
        e.element = self.element.where(clause).self_group()
        return e

class Join(FromClause):
    """represent a ``JOIN`` construct between two :class:`.FromClause`
    elements.

    The public constructor function for :class:`.Join` is the module-level
    :func:`join()` function, as well as the :func:`join()` method available
    off all :class:`.FromClause` subclasses.

    """
    __visit_name__ = 'join'

    def __init__(self, left, right, onclause=None, isouter=False):
        """Construct a new :class:`.Join`.

        The usual entrypoint here is the :func:`~.expression.join`
        function or the :meth:`.FromClause.join` method of any
        :class:`.FromClause` object.

        """
        self.left = _literal_as_text(left)
        self.right = _literal_as_text(right).self_group()

        if onclause is None:
            self.onclause = self._match_primaries(self.left, self.right)
        else:
            self.onclause = onclause

        self.isouter = isouter
        self.__folded_equivalents = None

    @property
    def description(self):
        return "Join object on %s(%d) and %s(%d)" % (
            self.left.description,
            id(self.left),
            self.right.description,
            id(self.right))

    def is_derived_from(self, fromclause):
        return fromclause is self or \
                self.left.is_derived_from(fromclause) or\
                self.right.is_derived_from(fromclause)

    def self_group(self, against=None):
        return _FromGrouping(self)

    def _populate_column_collection(self):
        columns = [c for c in self.left.columns] + \
                        [c for c in self.right.columns]

        self.primary_key.extend(sqlutil.reduce_columns(
                (c for c in columns if c.primary_key), self.onclause))
        self._columns.update((col._label, col) for col in columns)
        self.foreign_keys.update(itertools.chain(
                        *[col.foreign_keys for col in columns]))

    def _copy_internals(self, clone=_clone, **kw):
        self._reset_exported()
        self.left = clone(self.left, **kw)
        self.right = clone(self.right, **kw)
        self.onclause = clone(self.onclause, **kw)
        self.__folded_equivalents = None

    def get_children(self, **kwargs):
        return self.left, self.right, self.onclause

    def _match_primaries(self, left, right):
        if isinstance(left, Join):
            left_right = left.right
        else:
            left_right = None
        return sqlutil.join_condition(left, right, a_subset=left_right)

    def select(self, whereclause=None, fold_equivalents=False, **kwargs):
        """Create a :class:`.Select` from this :class:`.Join`.

        The equivalent long-hand form, given a :class:`.Join` object
        ``j``, is::

            from sqlalchemy import select
            j = select([j.left, j.right], **kw).\\
                        where(whereclause).\\
                        select_from(j)

        :param whereclause: the WHERE criterion that will be sent to 
          the :func:`select()` function

        :param fold_equivalents: based on the join criterion of this 
          :class:`.Join`, do not include
          repeat column names in the column list of the resulting
          select, for columns that are calculated to be "equivalent"
          based on the join criterion of this :class:`.Join`. This will
          recursively apply to any joins directly nested by this one
          as well.

        :param \**kwargs: all other kwargs are sent to the 
          underlying :func:`select()` function.

        """
        if fold_equivalents:
            collist = sqlutil.folded_equivalents(self)
        else:
            collist = [self.left, self.right]

        return select(collist, whereclause, from_obj=[self], **kwargs)

    @property
    def bind(self):
        return self.left.bind or self.right.bind

    def alias(self, name=None):
        """return an alias of this :class:`.Join`.

        Used against a :class:`.Join` object,
        :meth:`~.Join.alias` calls the :meth:`~.Join.select`
        method first so that a subquery against a 
        :func:`.select` construct is generated.
        the :func:`~expression.select` construct also has the 
        ``correlate`` flag set to ``False`` and will not
        auto-correlate inside an enclosing :func:`~expression.select`
        construct.

        The equivalent long-hand form, given a :class:`.Join` object
        ``j``, is::

            from sqlalchemy import select, alias
            j = alias(
                select([j.left, j.right]).\\
                    select_from(j).\\
                    with_labels(True).\\
                    correlate(False),
                name=name
            )

        See :func:`~.expression.alias` for further details on 
        aliases.

        """
        return self.select(use_labels=True, correlate=False).alias(name)

    @property
    def _hide_froms(self):
        return itertools.chain(*[_from_objects(x.left, x.right)
                               for x in self._cloned_set])

    @property
    def _from_objects(self):
        return [self] + \
                self.onclause._from_objects + \
                self.left._from_objects + \
                self.right._from_objects

class Alias(FromClause):
    """Represents an table or selectable alias (AS).

    Represents an alias, as typically applied to any table or
    sub-select within a SQL statement using the ``AS`` keyword (or
    without the keyword on certain databases such as Oracle).

    This object is constructed from the :func:`~.expression.alias` module level
    function as well as the :meth:`.FromClause.alias` method available on all
    :class:`.FromClause` subclasses.

    """

    __visit_name__ = 'alias'
    named_with_column = True

    def __init__(self, selectable, name=None):
        baseselectable = selectable
        while isinstance(baseselectable, Alias):
            baseselectable = baseselectable.element
        self.original = baseselectable
        self.supports_execution = baseselectable.supports_execution
        if self.supports_execution:
            self._execution_options = baseselectable._execution_options
        self.element = selectable
        if name is None:
            if self.original.named_with_column:
                name = getattr(self.original, 'name', None)
            name = _anonymous_label('%%(%d %s)s' % (id(self), name
                    or 'anon'))
        self.name = name

    @property
    def description(self):
        # Py3K
        #return self.name
        # Py2K
        return self.name.encode('ascii', 'backslashreplace')
        # end Py2K

    def as_scalar(self):
        try:
            return self.element.as_scalar()
        except AttributeError:
            raise AttributeError("Element %s does not support "
                                 "'as_scalar()'" % self.element)

    def is_derived_from(self, fromclause):
        if fromclause in self._cloned_set:
            return True
        return self.element.is_derived_from(fromclause)

    def _populate_column_collection(self):
        for col in self.element.columns:
            col._make_proxy(self)

    def _copy_internals(self, clone=_clone, **kw):
        # don't apply anything to an aliased Table
        # for now.   May want to drive this from
        # the given **kw.
        if isinstance(self.element, TableClause):
            return
        self._reset_exported()
        self.element = clone(self.element, **kw)
        baseselectable = self.element
        while isinstance(baseselectable, Alias):
            baseselectable = baseselectable.element
        self.original = baseselectable

    def get_children(self, column_collections=True, **kw):
        if column_collections:
            for c in self.c:
                yield c
        yield self.element

    @property
    def _from_objects(self):
        return [self]

    @property
    def bind(self):
        return self.element.bind

class CTE(Alias):
    """Represent a Common Table Expression.
    
    The :class:`.CTE` object is obtained using the
    :meth:`._SelectBase.cte` method from any selectable.
    See that method for complete examples.
    
    .. versionadded:: 0.7.6

    """
    __visit_name__ = 'cte'
    def __init__(self, selectable, 
                        name=None, 
                        recursive=False, 
                        cte_alias=False):
        self.recursive = recursive
        self.cte_alias = cte_alias
        super(CTE, self).__init__(selectable, name=name)

    def alias(self, name=None):
        return CTE(
            self.original,
            name=name,
            recursive=self.recursive,
            cte_alias = self.name
        )

    def union(self, other):
        return CTE(
            self.original.union(other),
            name=self.name,
            recursive=self.recursive
        )

    def union_all(self, other):
        return CTE(
            self.original.union_all(other),
            name=self.name,
            recursive=self.recursive
        )


class _Grouping(ColumnElement):
    """Represent a grouping within a column expression"""

    __visit_name__ = 'grouping'

    def __init__(self, element):
        self.element = element
        self.type = getattr(element, 'type', None)

    @property
    def _label(self):
        return getattr(self.element, '_label', None) or self.anon_label

    def _copy_internals(self, clone=_clone, **kw):
        self.element = clone(self.element, **kw)

    def get_children(self, **kwargs):
        return self.element,

    @property
    def _from_objects(self):
        return self.element._from_objects

    def __getattr__(self, attr):
        return getattr(self.element, attr)

    def __getstate__(self):
        return {'element':self.element, 'type':self.type}

    def __setstate__(self, state):
        self.element = state['element']
        self.type = state['type']

class _FromGrouping(FromClause):
    """Represent a grouping of a FROM clause"""
    __visit_name__ = 'grouping'

    def __init__(self, element):
        self.element = element

    def _init_collections(self):
        pass

    @property
    def columns(self):
        return self.element.columns

    @property
    def primary_key(self):
        return self.element.primary_key

    @property
    def foreign_keys(self):
        # this could be
        # self.element.foreign_keys
        # see SelectableTest.test_join_condition
        return set()

    @property
    def _hide_froms(self):
        return self.element._hide_froms

    def get_children(self, **kwargs):
        return self.element,

    def _copy_internals(self, clone=_clone, **kw):
        self.element = clone(self.element, **kw)

    @property
    def _from_objects(self):
        return self.element._from_objects

    def __getattr__(self, attr):
        return getattr(self.element, attr)

    def __getstate__(self):
        return {'element':self.element}

    def __setstate__(self, state):
        self.element = state['element']

class _Over(ColumnElement):
    """Represent an OVER clause.

    This is a special operator against a so-called 
    "window" function, as well as any aggregate function,
    which produces results relative to the result set
    itself.  It's supported only by certain database
    backends.

    """
    __visit_name__ = 'over'

    order_by = None
    partition_by = None

    def __init__(self, func, partition_by=None, order_by=None):
        self.func = func
        if order_by is not None:
            self.order_by = ClauseList(*util.to_list(order_by))
        if partition_by is not None:
            self.partition_by = ClauseList(*util.to_list(partition_by))

    @util.memoized_property
    def type(self):
        return self.func.type

    def get_children(self, **kwargs):
        return [c for c in 
                (self.func, self.partition_by, self.order_by) 
                if c is not None]

    def _copy_internals(self, clone=_clone, **kw):
        self.func = clone(self.func, **kw)
        if self.partition_by is not None:
            self.partition_by = clone(self.partition_by, **kw)
        if self.order_by is not None:
            self.order_by = clone(self.order_by, **kw)

    @property
    def _from_objects(self):
        return list(itertools.chain(
            *[c._from_objects for c in 
                (self.func, self.partition_by, self.order_by) 
            if c is not None]
        ))

class _Label(ColumnElement):
    """Represents a column label (AS).

    Represent a label, as typically applied to any column-level
    element using the ``AS`` sql keyword.

    This object is constructed from the :func:`label()` module level
    function as well as the :func:`label()` method available on all
    :class:`.ColumnElement` subclasses.

    """

    __visit_name__ = 'label'

    def __init__(self, name, element, type_=None):
        while isinstance(element, _Label):
            element = element.element
        if name:
            self.name = name
        else:
            self.name = _anonymous_label('%%(%d %s)s' % (id(self),
                                getattr(element, 'name', 'anon')))
        self.key = self._label = self._key_label = self.name
        self._element = element
        self._type = type_
        self.quote = element.quote
        self.proxies = [element]

    @util.memoized_property
    def type(self):
        return sqltypes.to_instance(
                    self._type or getattr(self._element, 'type', None)
                )

    @util.memoized_property
    def element(self):
        return self._element.self_group(against=operators.as_)

    def self_group(self, against=None):
        sub_element = self._element.self_group(against=against)
        if sub_element is not self._element:
            return _Label(self.name, 
                        sub_element, 
                        type_=self._type)
        else:
            return self

    @property
    def primary_key(self):
        return self.element.primary_key

    @property
    def foreign_keys(self):
        return self.element.foreign_keys

    def get_children(self, **kwargs):
        return self.element,

    def _copy_internals(self, clone=_clone, **kw):
        self.element = clone(self.element, **kw)

    @property
    def _from_objects(self):
        return self.element._from_objects

    def _make_proxy(self, selectable, name = None):
        e = self.element._make_proxy(selectable, name=name or self.name)
        e.proxies.append(self)
        return e

class ColumnClause(_Immutable, ColumnElement):
    """Represents a generic column expression from any textual string.

    This includes columns associated with tables, aliases and select
    statements, but also any arbitrary text.  May or may not be bound
    to an underlying :class:`.Selectable`.

    :class:`.ColumnClause` is constructed by itself typically via
    the :func:`~.expression.column` function.  It may be placed directly
    into constructs such as :func:`.select` constructs::

        from sqlalchemy.sql import column, select

        c1, c2 = column("c1"), column("c2")
        s = select([c1, c2]).where(c1==5)

    There is also a variant on :func:`~.expression.column` known
    as :func:`~.expression.literal_column` - the difference is that 
    in the latter case, the string value is assumed to be an exact
    expression, rather than a column name, so that no quoting rules
    or similar are applied::

        from sqlalchemy.sql import literal_column, select

        s = select([literal_column("5 + 7")])

    :class:`.ColumnClause` can also be used in a table-like 
    fashion by combining the :func:`~.expression.column` function 
    with the :func:`~.expression.table` function, to produce
    a "lightweight" form of table metadata::

        from sqlalchemy.sql import table, column

        user = table("user",
                column("id"),
                column("name"),
                column("description"),
        )

    The above construct can be created in an ad-hoc fashion and is
    not associated with any :class:`.schema.MetaData`, unlike it's
    more full fledged :class:`.schema.Table` counterpart.

    :param text: the text of the element.

    :param selectable: parent selectable.

    :param type: :class:`.types.TypeEngine` object which can associate 
      this :class:`.ColumnClause` with a type.

    :param is_literal: if True, the :class:`.ColumnClause` is assumed to 
      be an exact expression that will be delivered to the output with no
      quoting rules applied regardless of case sensitive settings. the
      :func:`literal_column()` function is usually used to create such a
      :class:`.ColumnClause`.

    """
    __visit_name__ = 'column'

    onupdate = default = server_default = server_onupdate = None

    _memoized_property = util.group_expirable_memoized_property() 

    def __init__(self, text, selectable=None, type_=None, is_literal=False):
        self.key = self.name = text
        self.table = selectable
        self.type = sqltypes.to_instance(type_)
        self.is_literal = is_literal

    def _compare_name_for_result(self, other):
        if self.table is not None and hasattr(other, 'proxy_set'):
            return other.proxy_set.intersection(self.proxy_set)
        else:
            return super(ColumnClause, self).\
                    _compare_name_for_result(other)

    def _get_table(self):
        return self.__dict__['table']
    def _set_table(self, table):
        self._memoized_property.expire_instance(self)
        self.__dict__['table'] = table
    table = property(_get_table, _set_table)

    @_memoized_property
    def _from_objects(self):
        t = self.table
        if t is not None:
            return [t]
        else:
            return []

    @util.memoized_property
    def description(self):
        # Py3K
        #return self.name
        # Py2K
        return self.name.encode('ascii', 'backslashreplace')
        # end Py2K

    @_memoized_property
    def _key_label(self):
        if self.key != self.name:
            return self._gen_label(self.key)
        else:
            return self._label

    @_memoized_property
    def _label(self):
        return self._gen_label(self.name)

    def _gen_label(self, name):
        t = self.table
        if self.is_literal:
            return None

        elif t is not None and t.named_with_column:
            if getattr(t, 'schema', None):
                label = t.schema.replace('.', '_') + "_" + \
                            t.name + "_" + name
            else:
                label = t.name + "_" + name

            # ensure the label name doesn't conflict with that
            # of an existing column
            if label in t.c:
                _label = label
                counter = 1
                while _label in t.c:
                    _label = label + "_" + str(counter)
                    counter += 1
                label = _label

            return _as_truncated(label)

        else:
            return name

    def label(self, name):
        # currently, anonymous labels don't occur for 
        # ColumnClause.   The use at the moment
        # is that they do not generate nicely for 
        # is_literal clauses.   We would like to change
        # this so that label(None) acts as would be expected.
        # See [ticket:2168].
        if name is None:
            return self
        else:
            return super(ColumnClause, self).label(name)


    def _bind_param(self, operator, obj):
        return _BindParamClause(self.name, obj,
                                _compared_to_operator=operator,
                                _compared_to_type=self.type,
                                unique=True)

    def _make_proxy(self, selectable, name=None, attach=True):
        # propagate the "is_literal" flag only if we are keeping our name,
        # otherwise its considered to be a label
        is_literal = self.is_literal and (name is None or name == self.name)
        c = self._constructor(
                    _as_truncated(name or self.name), 
                    selectable=selectable, 
                    type_=self.type, 
                    is_literal=is_literal
                )
        c.proxies = [self]
        if selectable._is_clone_of is not None:
            c._is_clone_of = \
                selectable._is_clone_of.columns.get(c.name)

        if attach:
            selectable._columns[c.name] = c
        return c

class TableClause(_Immutable, FromClause):
    """Represents a minimal "table" construct.

    The constructor for :class:`.TableClause` is the
    :func:`~.expression.table` function.   This produces 
    a lightweight table object that has only a name and a 
    collection of columns, which are typically produced
    by the :func:`~.expression.column` function::

        from sqlalchemy.sql import table, column

        user = table("user",
                column("id"),
                column("name"),
                column("description"),
        )

    The :class:`.TableClause` construct serves as the base for
    the more commonly used :class:`~.schema.Table` object, providing
    the usual set of :class:`~.expression.FromClause` services including
    the ``.c.`` collection and statement generation methods.

    It does **not** provide all the additional schema-level services
    of :class:`~.schema.Table`, including constraints, references to other 
    tables, or support for :class:`.MetaData`-level services.  It's useful
    on its own as an ad-hoc construct used to generate quick SQL
    statements when a more fully fledged :class:`~.schema.Table` is not on hand.

    """

    __visit_name__ = 'table'

    named_with_column = True

    def __init__(self, name, *columns):
        super(TableClause, self).__init__()
        self.name = self.fullname = name
        self._columns = ColumnCollection()
        self.primary_key = ColumnSet()
        self.foreign_keys = set()
        for c in columns:
            self.append_column(c)

    def _init_collections(self):
        pass

    @util.memoized_property
    def description(self):
        # Py3K
        #return self.name
        # Py2K
        return self.name.encode('ascii', 'backslashreplace')
        # end Py2K

    def append_column(self, c):
        self._columns[c.name] = c
        c.table = self

    def get_children(self, column_collections=True, **kwargs):
        if column_collections:
            return [c for c in self.c]
        else:
            return []

    def count(self, whereclause=None, **params):
        """return a SELECT COUNT generated against this
        :class:`.TableClause`."""

        if self.primary_key:
            col = list(self.primary_key)[0]
        else:
            col = list(self.columns)[0]
        return select(
                    [func.count(col).label('tbl_row_count')], 
                    whereclause, 
                    from_obj=[self], 
                    **params)

    def insert(self, values=None, inline=False, **kwargs):
        """Generate an :func:`.insert` construct against this
        :class:`.TableClause`.
        
        E.g.::
        
            table.insert().values(name='foo')
        
        See :func:`.insert` for argument and usage information.
        
        """

        return insert(self, values=values, inline=inline, **kwargs)

    def update(self, whereclause=None, values=None, inline=False, **kwargs):
        """Generate an :func:`.update` construct against this
        :class:`.TableClause`.
        
        E.g.::
        
            table.update().where(table.c.id==7).values(name='foo')
        
        See :func:`.update` for argument and usage information.
        
        """

        return update(self, whereclause=whereclause, 
                            values=values, inline=inline, **kwargs)

    def delete(self, whereclause=None, **kwargs):
        """Generate a :func:`.delete` construct against this
        :class:`.TableClause`.
        
        E.g.::
        
            table.delete().where(table.c.id==7)
        
        See :func:`.delete` for argument and usage information.
        
        """

        return delete(self, whereclause, **kwargs)

    @property
    def _from_objects(self):
        return [self]

class _SelectBase(Executable, FromClause):
    """Base class for :class:`.Select` and ``CompoundSelects``."""

    _order_by_clause = ClauseList()
    _group_by_clause = ClauseList()
    _limit = None
    _offset = None

    def __init__(self,
            use_labels=False,
            for_update=False,
            limit=None,
            offset=None,
            order_by=None,
            group_by=None,
            bind=None,
            autocommit=None):
        self.use_labels = use_labels
        self.for_update = for_update
        if autocommit is not None:
            util.warn_deprecated('autocommit on select() is '
                                 'deprecated.  Use .execution_options(a'
                                 'utocommit=True)')
            self._execution_options = \
                self._execution_options.union({'autocommit'
                    : autocommit})
        if limit is not None:
            self._limit = util.asint(limit)
        if offset is not None:
            self._offset = util.asint(offset)
        self._bind = bind

        if order_by is not None:
            self._order_by_clause = ClauseList(*util.to_list(order_by))
        if group_by is not None:
            self._group_by_clause = ClauseList(*util.to_list(group_by))

    def as_scalar(self):
        """return a 'scalar' representation of this selectable, which can be
        used as a column expression.

        Typically, a select statement which has only one column in its columns
        clause is eligible to be used as a scalar expression.

        The returned object is an instance of 
        :class:`_ScalarSelect`.

        """
        return _ScalarSelect(self)

    @_generative
    def apply_labels(self):
        """return a new selectable with the 'use_labels' flag set to True.

        This will result in column expressions being generated using labels
        against their table name, such as "SELECT somecolumn AS
        tablename_somecolumn". This allows selectables which contain multiple
        FROM clauses to produce a unique set of column names regardless of
        name conflicts among the individual FROM clauses.

        """
        self.use_labels = True

    def label(self, name):
        """return a 'scalar' representation of this selectable, embedded as a
        subquery with a label.

        See also :meth:`~._SelectBase.as_scalar`.

        """
        return self.as_scalar().label(name)

    def cte(self, name=None, recursive=False):
        """Return a new :class:`.CTE`, or Common Table Expression instance.
        
        Common table expressions are a SQL standard whereby SELECT
        statements can draw upon secondary statements specified along
        with the primary statement, using a clause called "WITH".
        Special semantics regarding UNION can also be employed to 
        allow "recursive" queries, where a SELECT statement can draw 
        upon the set of rows that have previously been selected.
        
        SQLAlchemy detects :class:`.CTE` objects, which are treated
        similarly to :class:`.Alias` objects, as special elements
        to be delivered to the FROM clause of the statement as well
        as to a WITH clause at the top of the statement.

        .. versionadded:: 0.7.6

        :param name: name given to the common table expression.  Like
         :meth:`._FromClause.alias`, the name can be left as ``None``
         in which case an anonymous symbol will be used at query
         compile time.
        :param recursive: if ``True``, will render ``WITH RECURSIVE``.
         A recursive common table expression is intended to be used in 
         conjunction with UNION ALL in order to derive rows
         from those already selected.

        The following examples illustrate two examples from 
        Postgresql's documentation at
        http://www.postgresql.org/docs/8.4/static/queries-with.html.
        
        Example 1, non recursive::
        
            from sqlalchemy import Table, Column, String, Integer, MetaData, \\
                select, func

            metadata = MetaData()

            orders = Table('orders', metadata,
                Column('region', String),
                Column('amount', Integer),
                Column('product', String),
                Column('quantity', Integer)
            )

            regional_sales = select([
                                orders.c.region, 
                                func.sum(orders.c.amount).label('total_sales')
                            ]).group_by(orders.c.region).cte("regional_sales")


            top_regions = select([regional_sales.c.region]).\\
                    where(
                        regional_sales.c.total_sales > 
                        select([
                            func.sum(regional_sales.c.total_sales)/10
                        ])
                    ).cte("top_regions")

            statement = select([
                        orders.c.region, 
                        orders.c.product, 
                        func.sum(orders.c.quantity).label("product_units"), 
                        func.sum(orders.c.amount).label("product_sales")
                ]).where(orders.c.region.in_(
                    select([top_regions.c.region])
                )).group_by(orders.c.region, orders.c.product)
        
            result = conn.execute(statement).fetchall()
            
        Example 2, WITH RECURSIVE::

            from sqlalchemy import Table, Column, String, Integer, MetaData, \\
                select, func

            metadata = MetaData()

            parts = Table('parts', metadata,
                Column('part', String),
                Column('sub_part', String),
                Column('quantity', Integer),
            )

            included_parts = select([
                                parts.c.sub_part, 
                                parts.c.part, 
                                parts.c.quantity]).\\
                                where(parts.c.part=='our part').\\
                                cte(recursive=True)


            incl_alias = included_parts.alias()
            parts_alias = parts.alias()
            included_parts = included_parts.union_all(
                select([
                    parts_alias.c.part, 
                    parts_alias.c.sub_part, 
                    parts_alias.c.quantity
                ]).
                    where(parts_alias.c.part==incl_alias.c.sub_part)
            )

            statement = select([
                        included_parts.c.sub_part, 
                        func.sum(included_parts.c.quantity).label('total_quantity')
                    ]).\
                    select_from(included_parts.join(parts,
                                included_parts.c.part==parts.c.part)).\\
                    group_by(included_parts.c.sub_part)

            result = conn.execute(statement).fetchall()

        
        See also:
        
        :meth:`.orm.query.Query.cte` - ORM version of :meth:`._SelectBase.cte`.

        """
        return CTE(self, name=name, recursive=recursive)

    @_generative
    @util.deprecated('0.6',
                     message=":func:`.autocommit` is deprecated. Use "
                     ":func:`.Executable.execution_options` with the "
                     "'autocommit' flag.")
    def autocommit(self):
        """return a new selectable with the 'autocommit' flag set to
        True."""

        self._execution_options = \
            self._execution_options.union({'autocommit': True})

    def _generate(self):
        """Override the default _generate() method to also clear out
        exported collections."""

        s = self.__class__.__new__(self.__class__)
        s.__dict__ = self.__dict__.copy()
        s._reset_exported()
        return s

    @_generative
    def limit(self, limit):
        """return a new selectable with the given LIMIT criterion
        applied."""

        self._limit = util.asint(limit)

    @_generative
    def offset(self, offset):
        """return a new selectable with the given OFFSET criterion
        applied."""

        self._offset = util.asint(offset)

    @_generative
    def order_by(self, *clauses):
        """return a new selectable with the given list of ORDER BY
        criterion applied.

        The criterion will be appended to any pre-existing ORDER BY
        criterion.

        """

        self.append_order_by(*clauses)

    @_generative
    def group_by(self, *clauses):
        """return a new selectable with the given list of GROUP BY
        criterion applied.

        The criterion will be appended to any pre-existing GROUP BY
        criterion.

        """

        self.append_group_by(*clauses)

    def append_order_by(self, *clauses):
        """Append the given ORDER BY criterion applied to this selectable.

        The criterion will be appended to any pre-existing ORDER BY criterion.

        """
        if len(clauses) == 1 and clauses[0] is None:
            self._order_by_clause = ClauseList()
        else:
            if getattr(self, '_order_by_clause', None) is not None:
                clauses = list(self._order_by_clause) + list(clauses)
            self._order_by_clause = ClauseList(*clauses)

    def append_group_by(self, *clauses):
        """Append the given GROUP BY criterion applied to this selectable.

        The criterion will be appended to any pre-existing GROUP BY criterion.

        """
        if len(clauses) == 1 and clauses[0] is None:
            self._group_by_clause = ClauseList()
        else:
            if getattr(self, '_group_by_clause', None) is not None:
                clauses = list(self._group_by_clause) + list(clauses)
            self._group_by_clause = ClauseList(*clauses)

    @property
    def _from_objects(self):
        return [self]


class _ScalarSelect(_Grouping):
    _from_objects = []

    def __init__(self, element):
        self.element = element
        self.type = element._scalar_type()

    @property
    def columns(self):
        raise exc.InvalidRequestError('Scalar Select expression has no '
                'columns; use this object directly within a '
                'column-level expression.')
    c = columns

    def self_group(self, **kwargs):
        return self

    def _make_proxy(self, selectable, name):
        return list(self.inner_columns)[0]._make_proxy(selectable, name)

class CompoundSelect(_SelectBase):
    """Forms the basis of ``UNION``, ``UNION ALL``, and other 
        SELECT-based set operations."""

    __visit_name__ = 'compound_select'

    UNION = util.symbol('UNION')
    UNION_ALL = util.symbol('UNION ALL')
    EXCEPT = util.symbol('EXCEPT')
    EXCEPT_ALL = util.symbol('EXCEPT ALL')
    INTERSECT = util.symbol('INTERSECT')
    INTERSECT_ALL = util.symbol('INTERSECT ALL')

    def __init__(self, keyword, *selects, **kwargs):
        self._should_correlate = kwargs.pop('correlate', False)
        self.keyword = keyword
        self.selects = []

        numcols = None

        # some DBs do not like ORDER BY in the inner queries of a UNION, etc.
        for n, s in enumerate(selects):
            s = _clause_element_as_expr(s)

            if not numcols:
                numcols = len(s.c)
            elif len(s.c) != numcols:
                raise exc.ArgumentError('All selectables passed to '
                        'CompoundSelect must have identical numbers of '
                        'columns; select #%d has %d columns, select '
                        '#%d has %d' % (1, len(self.selects[0].c), n
                        + 1, len(s.c)))

            self.selects.append(s.self_group(self))

        _SelectBase.__init__(self, **kwargs)

    def _scalar_type(self):
        return self.selects[0]._scalar_type()

    def self_group(self, against=None):
        return _FromGrouping(self)

    def is_derived_from(self, fromclause):
        for s in self.selects:
            if s.is_derived_from(fromclause):
                return True
        return False

    def _populate_column_collection(self):
        for cols in zip(*[s.c for s in self.selects]):

            # this is a slightly hacky thing - the union exports a
            # column that resembles just that of the *first* selectable.
            # to get at a "composite" column, particularly foreign keys,
            # you have to dig through the proxies collection which we
            # generate below.  We may want to improve upon this, such as
            # perhaps _make_proxy can accept a list of other columns
            # that are "shared" - schema.column can then copy all the
            # ForeignKeys in. this would allow the union() to have all
            # those fks too.

            proxy = cols[0]._make_proxy(self, name=self.use_labels
                    and cols[0]._label or None)

            # hand-construct the "proxies" collection to include all
            # derived columns place a 'weight' annotation corresponding
            # to how low in the list of select()s the column occurs, so
            # that the corresponding_column() operation can resolve
            # conflicts

            proxy.proxies = [c._annotate({'weight': i + 1}) for (i,
                             c) in enumerate(cols)]

    def _copy_internals(self, clone=_clone, **kw):
        self._reset_exported()
        self.selects = [clone(s, **kw) for s in self.selects]
        if hasattr(self, '_col_map'):
            del self._col_map
        for attr in ('_order_by_clause', '_group_by_clause'):
            if getattr(self, attr) is not None:
                setattr(self, attr, clone(getattr(self, attr), **kw))

    def get_children(self, column_collections=True, **kwargs):
        return (column_collections and list(self.c) or []) \
            + [self._order_by_clause, self._group_by_clause] \
            + list(self.selects)

    def bind(self):
        if self._bind:
            return self._bind
        for s in self.selects:
            e = s.bind
            if e:
                return e
        else:
            return None
    def _set_bind(self, bind):
        self._bind = bind
    bind = property(bind, _set_bind)

class Select(_SelectBase):
    """Represents a ``SELECT`` statement.

    See also:

    :func:`~.expression.select` - the function which creates a :class:`.Select` object.

    :ref:`coretutorial_selecting` - Core Tutorial description of :func:`.select`.

    """

    __visit_name__ = 'select'

    _prefixes = ()
    _hints = util.immutabledict()
    _distinct = False
    _from_cloned = None

    _memoized_property = _SelectBase._memoized_property

    def __init__(self, 
                columns, 
                whereclause=None, 
                from_obj=None, 
                distinct=False, 
                having=None, 
                correlate=True, 
                prefixes=None, 
                **kwargs):
        """Construct a Select object.

        The public constructor for Select is the
        :func:`select` function; see that function for
        argument descriptions.

        Additional generative and mutator methods are available on the
        :class:`_SelectBase` superclass.

        """
        self._should_correlate = correlate
        if distinct is not False:
            if isinstance(distinct, basestring):
                util.warn_deprecated(
                    "A string argument passed to the 'distinct' "
                    "keyword argument of 'select()' is deprecated "
                    "- please use 'prefixes' or 'prefix_with()' "
                    "to specify additional prefixes")
                if prefixes:
                    prefixes = util.to_list(prefixes) + [distinct]
                else:
                    prefixes = [distinct]
            elif distinct is True:
                self._distinct = True
            else:
                self._distinct = [
                                _literal_as_text(e) 
                                for e in util.to_list(distinct)
                            ]

        self._correlate = set()
        if from_obj is not None:
            self._from_obj = util.OrderedSet(
                                _literal_as_text(f) 
                                for f in util.to_list(from_obj))
        else:
            self._from_obj = util.OrderedSet()

        try:
            cols_present = bool(columns)
        except TypeError:
            raise exc.ArgumentError("columns argument to select() must "
                                "be a Python list or other iterable")

        if cols_present:
            self._raw_columns = []
            for c in columns:
                c = _literal_as_column(c)
                if isinstance(c, _ScalarSelect):
                    c = c.self_group(against=operators.comma_op)
                self._raw_columns.append(c)
        else:
            self._raw_columns = []

        if whereclause is not None:
            self._whereclause = _literal_as_text(whereclause)
        else:
            self._whereclause = None

        if having is not None:
            self._having = _literal_as_text(having)
        else:
            self._having = None

        if prefixes:
            self._prefixes = tuple([_literal_as_text(p) for p in prefixes])

        _SelectBase.__init__(self, **kwargs)

    @property
    def _froms(self):
        # would love to cache this,
        # but there's just enough edge cases, particularly now that
        # declarative encourages construction of SQL expressions 
        # without tables present, to just regen this each time.
        froms = []
        seen = set()
        translate = self._from_cloned
        def add(items):
            for item in items:
                if translate and item in translate:
                    item = translate[item]
                if not seen.intersection(item._cloned_set):
                    froms.append(item)
                seen.update(item._cloned_set)

        add(_from_objects(*self._raw_columns))
        if self._whereclause is not None:
            add(_from_objects(self._whereclause))
        add(self._from_obj)

        return froms

    def _get_display_froms(self, existing_froms=None):
        """Return the full list of 'from' clauses to be displayed.

        Takes into account a set of existing froms which may be
        rendered in the FROM clause of enclosing selects; this Select
        may want to leave those absent if it is automatically
        correlating.

        """
        froms = self._froms

        toremove = set(itertools.chain(*[f._hide_froms for f in froms]))
        if toremove:
            # if we're maintaining clones of froms,
            # add the copies out to the toremove list
            if self._from_cloned:
                toremove.update(
                    self._from_cloned[f] for f in 
                    toremove.intersection(self._from_cloned)
                )
            # filter out to FROM clauses not in the list,
            # using a list to maintain ordering
            froms = [f for f in froms if f not in toremove]

        if len(froms) > 1 or self._correlate:
            if self._correlate:
                froms = [f for f in froms if f not in _cloned_intersection(froms,
                        self._correlate)]
            if self._should_correlate and existing_froms:
                froms = [f for f in froms if f not in _cloned_intersection(froms,
                        existing_froms)]

                if not len(froms):
                    raise exc.InvalidRequestError("Select statement '%s"
                            "' returned no FROM clauses due to "
                            "auto-correlation; specify "
                            "correlate(<tables>) to control "
                            "correlation manually." % self)

        return froms

    def _scalar_type(self):
        elem = self._raw_columns[0]
        cols = list(elem._select_iterable)
        return cols[0].type

    @property
    def froms(self):
        """Return the displayed list of FromClause elements."""

        return self._get_display_froms()

    @_generative
    def with_hint(self, selectable, text, dialect_name='*'):
        """Add an indexing hint for the given selectable to this
        :class:`.Select`.

        The text of the hint is rendered in the appropriate
        location for the database backend in use, relative
        to the given :class:`.Table` or :class:`.Alias` passed as the
        ``selectable`` argument. The dialect implementation
        typically uses Python string substitution syntax
        with the token ``%(name)s`` to render the name of
        the table or alias. E.g. when using Oracle, the
        following::

            select([mytable]).\\
                with_hint(mytable, "+ index(%(name)s ix_mytable)")

        Would render SQL as::

            select /*+ index(mytable ix_mytable) */ ... from mytable

        The ``dialect_name`` option will limit the rendering of a particular
        hint to a particular backend. Such as, to add hints for both Oracle
        and Sybase simultaneously::

            select([mytable]).\\
                with_hint(mytable, "+ index(%(name)s ix_mytable)", 'oracle').\\
                with_hint(mytable, "WITH INDEX ix_mytable", 'sybase')

        """
        self._hints = self._hints.union({(selectable, dialect_name):text})

    @property
    def type(self):
        raise exc.InvalidRequestError("Select objects don't have a type.  "
                    "Call as_scalar() on this Select object "
                    "to return a 'scalar' version of this Select.")

    @_memoized_property.method
    def locate_all_froms(self):
        """return a Set of all FromClause elements referenced by this Select.

        This set is a superset of that returned by the ``froms`` property,
        which is specifically for those FromClause elements that would
        actually be rendered.

        """
        froms = self._froms
        return froms + list(_from_objects(*froms))

    @property
    def inner_columns(self):
        """an iterator of all ColumnElement expressions which would
        be rendered into the columns clause of the resulting SELECT statement.

        """
        return _select_iterables(self._raw_columns)

    def is_derived_from(self, fromclause):
        if self in fromclause._cloned_set:
            return True

        for f in self.locate_all_froms():
            if f.is_derived_from(fromclause):
                return True
        return False

    def _copy_internals(self, clone=_clone, **kw):

        # Select() object has been cloned and probably adapted by the
        # given clone function.  Apply the cloning function to internal
        # objects

        # 1. keep a dictionary of the froms we've cloned, and what
        # they've become.  This is consulted later when we derive
        # additional froms from "whereclause" and the columns clause,
        # which may still reference the uncloned parent table.
        # as of 0.7.4 we also put the current version of _froms, which
        # gets cleared on each generation.  previously we were "baking"
        # _froms into self._from_obj.
        self._from_cloned = from_cloned = dict((f, clone(f, **kw))
                for f in self._from_obj.union(self._froms))

        # 3. update persistent _from_obj with the cloned versions.
        self._from_obj = util.OrderedSet(from_cloned[f] for f in
                self._from_obj)

        # the _correlate collection is done separately, what can happen
        # here is the same item is _correlate as in _from_obj but the
        # _correlate version has an annotation on it - (specifically
        # RelationshipProperty.Comparator._criterion_exists() does
        # this). Also keep _correlate liberally open with it's previous
        # contents, as this set is used for matching, not rendering.
        self._correlate = set(clone(f) for f in
                              self._correlate).union(self._correlate)

        # 4. clone other things.   The difficulty here is that Column
        # objects are not actually cloned, and refer to their original
        # .table, resulting in the wrong "from" parent after a clone
        # operation.  Hence _from_cloned and _from_obj supercede what is
        # present here.
        self._raw_columns = [clone(c, **kw) for c in self._raw_columns]
        for attr in '_whereclause', '_having', '_order_by_clause', \
            '_group_by_clause':
            if getattr(self, attr) is not None:
                setattr(self, attr, clone(getattr(self, attr), **kw))

        # erase exported column list, _froms collection,
        # etc.
        self._reset_exported()

    def get_children(self, column_collections=True, **kwargs):
        """return child elements as per the ClauseElement specification."""

        return (column_collections and list(self.columns) or []) + \
            self._raw_columns + list(self._froms) + \
            [x for x in 
                (self._whereclause, self._having, 
                    self._order_by_clause, self._group_by_clause) 
            if x is not None]

    @_generative
    def column(self, column):
        """return a new select() construct with the given column expression 
            added to its columns clause.

        """
        self.append_column(column)

    @_generative
    def with_only_columns(self, columns):
        """Return a new :func:`.select` construct with its columns 
        clause replaced with the given columns.
        
        .. versionchanged:: 0.7.3
            Due to a bug fix, this method has a slight 
            behavioral change as of version 0.7.3.  
            Prior to version 0.7.3, the FROM clause of 
            a :func:`.select` was calculated upfront and as new columns
            were added; in 0.7.3 and later it's calculated 
            at compile time, fixing an issue regarding late binding
            of columns to parent tables.  This changes the behavior of 
            :meth:`.Select.with_only_columns` in that FROM clauses no
            longer represented in the new list are dropped, 
            but this behavior is more consistent in 
            that the FROM clauses are consistently derived from the
            current columns clause.  The original intent of this method
            is to allow trimming of the existing columns list to be fewer
            columns than originally present; the use case of replacing
            the columns list with an entirely different one hadn't
            been anticipated until 0.7.3 was released; the usage
            guidelines below illustrate how this should be done.

        This method is exactly equivalent to as if the original 
        :func:`.select` had been called with the given columns 
        clause.   I.e. a statement::
        
            s = select([table1.c.a, table1.c.b])
            s = s.with_only_columns([table1.c.b])
            
        should be exactly equivalent to::
        
            s = select([table1.c.b])
        
        This means that FROM clauses which are only derived 
        from the column list will be discarded if the new column 
        list no longer contains that FROM::
        
            >>> table1 = table('t1', column('a'), column('b'))
            >>> table2 = table('t2', column('a'), column('b'))
            >>> s1 = select([table1.c.a, table2.c.b])
            >>> print s1
            SELECT t1.a, t2.b FROM t1, t2
            >>> s2 = s1.with_only_columns([table2.c.b])
            >>> print s2
            SELECT t2.b FROM t1
        
        The preferred way to maintain a specific FROM clause
        in the construct, assuming it won't be represented anywhere
        else (i.e. not in the WHERE clause, etc.) is to set it using 
        :meth:`.Select.select_from`::
        
            >>> s1 = select([table1.c.a, table2.c.b]).\\
            ...         select_from(table1.join(table2, table1.c.a==table2.c.a))
            >>> s2 = s1.with_only_columns([table2.c.b])
            >>> print s2
            SELECT t2.b FROM t1 JOIN t2 ON t1.a=t2.a
            
        Care should also be taken to use the correct
        set of column objects passed to :meth:`.Select.with_only_columns`.
        Since the method is essentially equivalent to calling the
        :func:`.select` construct in the first place with the given 
        columns, the columns passed to :meth:`.Select.with_only_columns` 
        should usually be a subset of those which were passed 
        to the :func:`.select` construct, not those which are available
        from the ``.c`` collection of that :func:`.select`.  That
        is::
        
            s = select([table1.c.a, table1.c.b]).select_from(table1)
            s = s.with_only_columns([table1.c.b])
        
        and **not**::
        
            # usually incorrect
            s = s.with_only_columns([s.c.b])

        The latter would produce the SQL::

            SELECT b 
            FROM (SELECT t1.a AS a, t1.b AS b 
            FROM t1), t1
        
        Since the :func:`.select` construct is essentially being
        asked to select both from ``table1`` as well as itself.
        
        """
        self._reset_exported()
        rc = []
        for c in columns:
            c = _literal_as_column(c)
            if isinstance(c, _ScalarSelect):
                c = c.self_group(against=operators.comma_op)
            rc.append(c)
        self._raw_columns = rc

    @_generative
    def where(self, whereclause):
        """return a new select() construct with the given expression added to
        its WHERE clause, joined to the existing clause via AND, if any.

        """

        self.append_whereclause(whereclause)

    @_generative
    def having(self, having):
        """return a new select() construct with the given expression added to
        its HAVING clause, joined to the existing clause via AND, if any.

        """
        self.append_having(having)

    @_generative
    def distinct(self, *expr):
        """Return a new select() construct which will apply DISTINCT to its
        columns clause.

        :param \*expr: optional column expressions.  When present,
         the Postgresql dialect will render a ``DISTINCT ON (<expressions>>)``
         construct.

        """
        if expr:
            expr = [_literal_as_text(e) for e in expr]
            if isinstance(self._distinct, list):
                self._distinct = self._distinct + expr
            else:
                self._distinct = expr
        else:
            self._distinct = True

    @_generative
    def prefix_with(self, *expr):
        """return a new select() construct which will apply the given
        expressions, typically strings, to the start of its columns clause, 
        not using any commas.   In particular is useful for MySQL
        keywords.

        e.g.::

             select(['a', 'b']).prefix_with('HIGH_PRIORITY', 
                                    'SQL_SMALL_RESULT', 
                                    'ALL')

        Would render::

            SELECT HIGH_PRIORITY SQL_SMALL_RESULT ALL a, b

         """
        expr = tuple(_literal_as_text(e) for e in expr)
        self._prefixes = self._prefixes + expr

    @_generative
    def select_from(self, fromclause):
        """return a new :func:`.select` construct with the given FROM expression
        merged into its list of FROM objects.
        
        E.g.::
        
            table1 = table('t1', column('a'))
            table2 = table('t2', column('b'))
            s = select([table1.c.a]).\\
                select_from(
                    table1.join(table2, table1.c.a==table2.c.b)
                )
        
        The "from" list is a unique set on the identity of each element,
        so adding an already present :class:`.Table` or other selectable
        will have no effect.   Passing a :class:`.Join` that refers
        to an already present :class:`.Table` or other selectable will have 
        the effect of concealing the presence of that selectable as 
        an individual element in the rendered FROM list, instead rendering it into a
        JOIN clause.
        
        While the typical purpose of :meth:`.Select.select_from` is to replace
        the default, derived FROM clause with a join, it can also be called with
        individual table elements, multiple times if desired, in the case that the 
        FROM clause cannot be fully derived from the columns clause::
        
            select([func.count('*')]).select_from(table1)
        
        """
        self.append_from(fromclause)

    @_generative
    def correlate(self, *fromclauses):
        """return a new select() construct which will correlate the given FROM
        clauses to that of an enclosing select(), if a match is found.

        By "match", the given fromclause must be present in this select's
        list of FROM objects and also present in an enclosing select's list of
        FROM objects.

        Calling this method turns off the select's default behavior of
        "auto-correlation". Normally, select() auto-correlates all of its FROM
        clauses to those of an embedded select when compiled.

        If the fromclause is None, correlation is disabled for the returned
        select().

        """
        self._should_correlate = False
        if fromclauses and fromclauses[0] is None:
            self._correlate = set()
        else:
            self._correlate = self._correlate.union(fromclauses)

    def append_correlation(self, fromclause):
        """append the given correlation expression to this select()
        construct."""

        self._should_correlate = False
        self._correlate = self._correlate.union([fromclause])

    def append_column(self, column):
        """append the given column expression to the columns clause of this
        select() construct.

        """
        self._reset_exported()
        column = _literal_as_column(column)

        if isinstance(column, _ScalarSelect):
            column = column.self_group(against=operators.comma_op)

        self._raw_columns = self._raw_columns + [column]

    def append_prefix(self, clause):
        """append the given columns clause prefix expression to this select()
        construct.

        """
        clause = _literal_as_text(clause)
        self._prefixes = self._prefixes + (clause,)

    def append_whereclause(self, whereclause):
        """append the given expression to this select() construct's WHERE
        criterion.

        The expression will be joined to existing WHERE criterion via AND.

        """
        self._reset_exported()
        whereclause = _literal_as_text(whereclause)

        if self._whereclause is not None:
            self._whereclause = and_(self._whereclause, whereclause)
        else:
            self._whereclause = whereclause

    def append_having(self, having):
        """append the given expression to this select() construct's HAVING
        criterion.

        The expression will be joined to existing HAVING criterion via AND.

        """
        if self._having is not None:
            self._having = and_(self._having, _literal_as_text(having))
        else:
            self._having = _literal_as_text(having)

    def append_from(self, fromclause):
        """append the given FromClause expression to this select() construct's
        FROM clause.

        """
        self._reset_exported()
        fromclause = _literal_as_text(fromclause)
        self._from_obj = self._from_obj.union([fromclause])

    def _populate_column_collection(self):
        for c in self.inner_columns:
            if hasattr(c, '_make_proxy'):
                c._make_proxy(self, 
                        name=self.use_labels 
                            and c._label or None)

    def self_group(self, against=None):
        """return a 'grouping' construct as per the ClauseElement
        specification.

        This produces an element that can be embedded in an expression. Note
        that this method is called automatically as needed when constructing
        expressions and should not require explicit use.

        """
        if isinstance(against, CompoundSelect):
            return self
        return _FromGrouping(self)

    def union(self, other, **kwargs):
        """return a SQL UNION of this select() construct against the given
        selectable."""

        return union(self, other, **kwargs)

    def union_all(self, other, **kwargs):
        """return a SQL UNION ALL of this select() construct against the given
        selectable.

        """
        return union_all(self, other, **kwargs)

    def except_(self, other, **kwargs):
        """return a SQL EXCEPT of this select() construct against the given
        selectable."""

        return except_(self, other, **kwargs)

    def except_all(self, other, **kwargs):
        """return a SQL EXCEPT ALL of this select() construct against the
        given selectable.

        """
        return except_all(self, other, **kwargs)

    def intersect(self, other, **kwargs):
        """return a SQL INTERSECT of this select() construct against the given
        selectable.

        """
        return intersect(self, other, **kwargs)

    def intersect_all(self, other, **kwargs):
        """return a SQL INTERSECT ALL of this select() construct against the
        given selectable.

        """
        return intersect_all(self, other, **kwargs)

    def bind(self):
        if self._bind:
            return self._bind
        froms = self._froms
        if not froms:
            for c in self._raw_columns:
                e = c.bind
                if e:
                    self._bind = e
                    return e
        else:
            e = list(froms)[0].bind
            if e:
                self._bind = e
                return e

        return None

    def _set_bind(self, bind):
        self._bind = bind
    bind = property(bind, _set_bind)

class UpdateBase(Executable, ClauseElement):
    """Form the base for ``INSERT``, ``UPDATE``, and ``DELETE`` statements.

    """

    __visit_name__ = 'update_base'

    _execution_options = \
        Executable._execution_options.union({'autocommit': True})
    kwargs = util.immutabledict()
    _hints = util.immutabledict()

    def _process_colparams(self, parameters):
        if isinstance(parameters, (list, tuple)):
            pp = {}
            for i, c in enumerate(self.table.c):
                pp[c.key] = parameters[i]
            return pp
        else:
            return parameters

    def params(self, *arg, **kw):
        """Set the parameters for the statement.

        This method raises ``NotImplementedError`` on the base class,
        and is overridden by :class:`.ValuesBase` to provide the
        SET/VALUES clause of UPDATE and INSERT.

        """
        raise NotImplementedError(
            "params() is not supported for INSERT/UPDATE/DELETE statements."
            " To set the values for an INSERT or UPDATE statement, use"
            " stmt.values(**parameters).")

    def bind(self):
        """Return a 'bind' linked to this :class:`.UpdateBase`
        or a :class:`.Table` associated with it.

        """
        return self._bind or self.table.bind

    def _set_bind(self, bind):
        self._bind = bind
    bind = property(bind, _set_bind)

    _returning_re = re.compile(r'(?:firebird|postgres(?:ql)?)_returning')
    def _process_deprecated_kw(self, kwargs):
        for k in list(kwargs):
            m = self._returning_re.match(k)
            if m:
                self._returning = kwargs.pop(k)
                util.warn_deprecated(
                    "The %r argument is deprecated.  Please "
                    "use statement.returning(col1, col2, ...)" % k
                )
        return kwargs

    @_generative
    def returning(self, *cols):
        """Add a RETURNING or equivalent clause to this statement.

        The given list of columns represent columns within the table that is
        the target of the INSERT, UPDATE, or DELETE. Each element can be any
        column expression. :class:`~sqlalchemy.schema.Table` objects will be
        expanded into their individual columns.

        Upon compilation, a RETURNING clause, or database equivalent, 
        will be rendered within the statement.   For INSERT and UPDATE, 
        the values are the newly inserted/updated values.  For DELETE, 
        the values are those of the rows which were deleted.

        Upon execution, the values of the columns to be returned
        are made available via the result set and can be iterated
        using ``fetchone()`` and similar.   For DBAPIs which do not
        natively support returning values (i.e. cx_oracle), 
        SQLAlchemy will approximate this behavior at the result level
        so that a reasonable amount of behavioral neutrality is 
        provided.

        Note that not all databases/DBAPIs
        support RETURNING.   For those backends with no support,
        an exception is raised upon compilation and/or execution.
        For those who do support it, the functionality across backends
        varies greatly, including restrictions on executemany()
        and other statements which return multiple rows. Please 
        read the documentation notes for the database in use in 
        order to determine the availability of RETURNING.

        """
        self._returning = cols

    @_generative
    def with_hint(self, text, selectable=None, dialect_name="*"):
        """Add a table hint for a single table to this 
        INSERT/UPDATE/DELETE statement.

        .. note::

         :meth:`.UpdateBase.with_hint` currently applies only to 
         Microsoft SQL Server.  For MySQL INSERT hints, use
         :meth:`.Insert.prefix_with`.   UPDATE/DELETE hints for 
         MySQL will be added in a future release.
         
        The text of the hint is rendered in the appropriate
        location for the database backend in use, relative
        to the :class:`.Table` that is the subject of this
        statement, or optionally to that of the given 
        :class:`.Table` passed as the ``selectable`` argument.

        The ``dialect_name`` option will limit the rendering of a particular
        hint to a particular backend. Such as, to add a hint
        that only takes effect for SQL Server::

            mytable.insert().with_hint("WITH (PAGLOCK)", dialect_name="mssql")

        .. versionadded:: 0.7.6

        :param text: Text of the hint.
        :param selectable: optional :class:`.Table` that specifies
         an element of the FROM clause within an UPDATE or DELETE
         to be the subject of the hint - applies only to certain backends.
        :param dialect_name: defaults to ``*``, if specified as the name
         of a particular dialect, will apply these hints only when
         that dialect is in use.
         """
        if selectable is None:
            selectable = self.table

        self._hints = self._hints.union({(selectable, dialect_name):text})

class ValuesBase(UpdateBase):
    """Supplies support for :meth:`.ValuesBase.values` to INSERT and UPDATE constructs."""

    __visit_name__ = 'values_base'

    def __init__(self, table, values):
        self.table = table
        self.parameters = self._process_colparams(values)

    @_generative
    def values(self, *args, **kwargs):
        """specify the VALUES clause for an INSERT statement, or the SET
        clause for an UPDATE.

        :param \**kwargs: key value pairs representing the string key 
          of a :class:`.Column` mapped to the value to be rendered into the
          VALUES or SET clause::

                users.insert().values(name="some name")

                users.update().where(users.c.id==5).values(name="some name")

        :param \*args: A single dictionary can be sent as the first positional
            argument. This allows non-string based keys, such as Column
            objects, to be used::

                users.insert().values({users.c.name : "some name"})

                users.update().where(users.c.id==5).values({users.c.name : "some name"})

        See also:

            :ref:`inserts_and_updates` - SQL Expression 
            Language Tutorial

            :func:`~.expression.insert` - produce an ``INSERT`` statement

            :func:`~.expression.update` - produce an ``UPDATE`` statement
        
        """
        if args:
            v = args[0]
        else:
            v = {}

        if self.parameters is None:
            self.parameters = self._process_colparams(v)
            self.parameters.update(kwargs)
        else:
            self.parameters = self.parameters.copy()
            self.parameters.update(self._process_colparams(v))
            self.parameters.update(kwargs)

class Insert(ValuesBase):
    """Represent an INSERT construct.

    The :class:`.Insert` object is created using the :func:`~.expression.insert()` function.

    See also:

    :ref:`coretutorial_insert_expressions`

    """
    __visit_name__ = 'insert'

    _prefixes = ()

    def __init__(self, 
                table, 
                values=None, 
                inline=False, 
                bind=None, 
                prefixes=None, 
                returning=None,
                **kwargs):
        ValuesBase.__init__(self, table, values)
        self._bind = bind
        self.select = None
        self.inline = inline
        self._returning = returning
        if prefixes:
            self._prefixes = tuple([_literal_as_text(p) for p in prefixes])

        if kwargs:
            self.kwargs = self._process_deprecated_kw(kwargs)

    def get_children(self, **kwargs):
        if self.select is not None:
            return self.select,
        else:
            return ()

    def _copy_internals(self, clone=_clone, **kw):
        # TODO: coverage
        self.parameters = self.parameters.copy()

    @_generative
    def prefix_with(self, clause):
        """Add a word or expression between INSERT and INTO. Generative.

        If multiple prefixes are supplied, they will be separated with
        spaces.

        """
        clause = _literal_as_text(clause)
        self._prefixes = self._prefixes + (clause,)

class Update(ValuesBase):
    """Represent an Update construct.

    The :class:`.Update` object is created using the :func:`update()` function.

    """
    __visit_name__ = 'update'

    def __init__(self, 
                table, 
                whereclause, 
                values=None, 
                inline=False, 
                bind=None, 
                returning=None,
                **kwargs):
        ValuesBase.__init__(self, table, values)
        self._bind = bind
        self._returning = returning
        if whereclause is not None:
            self._whereclause = _literal_as_text(whereclause)
        else:
            self._whereclause = None
        self.inline = inline

        if kwargs:
            self.kwargs = self._process_deprecated_kw(kwargs)

    def get_children(self, **kwargs):
        if self._whereclause is not None:
            return self._whereclause,
        else:
            return ()

    def _copy_internals(self, clone=_clone, **kw):
        # TODO: coverage
        self._whereclause = clone(self._whereclause, **kw)
        self.parameters = self.parameters.copy()

    @_generative
    def where(self, whereclause):
        """return a new update() construct with the given expression added to
        its WHERE clause, joined to the existing clause via AND, if any.

        """
        if self._whereclause is not None:
            self._whereclause = and_(self._whereclause,
                    _literal_as_text(whereclause))
        else:
            self._whereclause = _literal_as_text(whereclause)

    @property
    def _extra_froms(self):
        # TODO: this could be made memoized
        # if the memoization is reset on each generative call.
        froms = []
        seen = set([self.table])

        if self._whereclause is not None:
            for item in _from_objects(self._whereclause):
                if not seen.intersection(item._cloned_set):
                    froms.append(item)
                seen.update(item._cloned_set)

        return froms

class Delete(UpdateBase):
    """Represent a DELETE construct.

    The :class:`.Delete` object is created using the :func:`delete()` function.

    """

    __visit_name__ = 'delete'

    def __init__(self, 
            table, 
            whereclause, 
            bind=None, 
            returning =None,
            **kwargs):
        self._bind = bind
        self.table = table
        self._returning = returning

        if whereclause is not None:
            self._whereclause = _literal_as_text(whereclause)
        else:
            self._whereclause = None

        if kwargs:
            self.kwargs = self._process_deprecated_kw(kwargs)

    def get_children(self, **kwargs):
        if self._whereclause is not None:
            return self._whereclause,
        else:
            return ()

    @_generative
    def where(self, whereclause):
        """Add the given WHERE clause to a newly returned delete construct."""

        if self._whereclause is not None:
            self._whereclause = and_(self._whereclause,
                    _literal_as_text(whereclause))
        else:
            self._whereclause = _literal_as_text(whereclause)

    def _copy_internals(self, clone=_clone, **kw):
        # TODO: coverage
        self._whereclause = clone(self._whereclause, **kw)

class _IdentifiedClause(Executable, ClauseElement):

    __visit_name__ = 'identified'
    _execution_options = \
        Executable._execution_options.union({'autocommit': False})
    quote = None

    def __init__(self, ident):
        self.ident = ident

class SavepointClause(_IdentifiedClause):
    __visit_name__ = 'savepoint'

class RollbackToSavepointClause(_IdentifiedClause):
    __visit_name__ = 'rollback_to_savepoint'

class ReleaseSavepointClause(_IdentifiedClause):
    __visit_name__ = 'release_savepoint'