Source

sqlalchemy / lib / sqlalchemy / sql / elements.py

   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
# sql/elements.py
# Copyright (C) 2005-2013 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

"""Core SQL expression elements, including :class:`.ClauseElement`,
:class:`.ColumnElement`, and derived classes.

"""

from __future__ import unicode_literals

from .. import util, exc, inspection
from . import type_api
from . import operators
from .visitors import Visitable, cloned_traverse, traverse
from .annotation import Annotated
import itertools
from .base import Executable, PARSE_AUTOCOMMIT, Immutable, NO_ARG
import re
import operator

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

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

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

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

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

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:`.ColumnElement`
    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:`BindParameter` 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 BindParameter(None, value, type_=type_, unique=True)



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')
                    )
        )

    """
    type_ = type_api.to_instance(type_)

    if hasattr(expr, '__clause_expr__'):
        return type_coerce(expr.__clause_expr__())
    elif isinstance(expr, BindParameter):
        bp = expr._clone()
        bp.type = type_
        return bp
    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 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 BindParameter(
                key, None, type_=type_, unique=False, isoutparam=True)


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

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

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



@inspection._self_inspects
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
    is_selectable = False
    is_clause_element = True

    _order_by_label_element = 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()
        ClauseElement._cloned_set._reset(c)
        ColumnElement.comparator._reset(c)

        # 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

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

        """
        return Annotated(self, values)

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

        """
        return Annotated(self, values)

    def _deannotate(self, values=None, clone=False):
        """return a copy of this :class:`.ClauseElement` with annotations
        removed.

        :param values: optional tuple of individual values
         to remove.

        """
        if clone:
            # clone is used when we are also copying
            # the expression for a deep deannotation
            return self._clone()
        else:
            # if no clone, since we have no annotations we return
            # self
            return self

    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]
                bind.required = False
            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.dependencies("sqlalchemy.engine.default")
    def compile(self, default, bind=None, dialect=None, **kw):
        """Compile this SQL expression.

        The return value is a :class:`~.Compiled` object.
        Calling ``str()`` or ``unicode()`` on the returned value will yield a
        string representation of the result. The
        :class:`~.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):
        if util.py3k:
            return str(self.compile())
        else:
            return unicode(self.compile()).encode('ascii', 'backslashreplace')

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

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

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

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

    __nonzero__ = __bool__

    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 ColumnElement(ClauseElement, operators.ColumnOperators):
    """Represent a column-oriented SQL expression suitable for usage in the
    "columns" clause, WHERE clause etc. of a statement.

    While the most familiar kind of :class:`.ColumnElement` is the
    :class:`.Column` object, :class:`.ColumnElement` serves as the basis
    for any unit that may be present in a SQL expression, including
    the expressions themselves, SQL functions, bound parameters,
    literal expressions, keywords such as ``NULL``, etc.
    :class:`.ColumnElement` is the ultimate base class for all such elements.

    A :class:`.ColumnElement` provides the ability to generate new
    :class:`.ColumnElement`
    objects using Python expressions.  This means that Python operators
    such as ``==``, ``!=`` and ``<`` are overloaded to mimic SQL operations,
    and allow the instantiation of further :class:`.ColumnElement` instances
    which are composed from other, more fundamental :class:`.ColumnElement`
    objects.  For example, two :class:`.ColumnClause` objects can be added
    together with the addition operator ``+`` to produce
    a :class:`.BinaryExpression`.
    Both :class:`.ColumnClause` and :class:`.BinaryExpression` are subclasses
    of :class:`.ColumnElement`::

        >>> from sqlalchemy.sql import column
        >>> column('a') + column('b')
        <sqlalchemy.sql.expression.BinaryExpression object at 0x101029dd0>
        >>> print column('a') + column('b')
        a + b

    :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`.  For the ambitious, an in-depth
    discussion of this concept can be found at
    `Expression Transformations <http://techspot.zzzeek.org/2008/01/23/expression-transformations/>`_.

    """

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

    @util.memoized_property
    def type(self):
        return type_api.NULLTYPE

    @util.memoized_property
    def comparator(self):
        return self.type.comparator_factory(self)

    def __getattr__(self, key):
        try:
            return getattr(self.comparator, key)
        except AttributeError:
            raise AttributeError(
                    'Neither %r object nor %r object has an attribute %r' % (
                    type(self).__name__,
                    type(self.comparator).__name__,
                    key)
            )

    def operate(self, op, *other, **kwargs):
        return op(self.comparator, *other, **kwargs)

    def reverse_operate(self, op, other, **kwargs):
        return op(other, self.comparator, **kwargs)

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

    @property
    def expression(self):
        """Return a column expression.

        Part of the inspection interface; returns self.

        """
        return self

    @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, name_is_truncatable=False, **kw):
        """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
            try:
                key = str(self)
            except exc.UnsupportedCompilationError:
                key = self.anon_label
        else:
            key = name
        co = ColumnClause(
                _as_truncated(name) if name_is_truncatable else name,
                type_=getattr(self, 'type', None),
                _selectable=selectable
            )
        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 hash(oth) == hash(self):
                return True
        else:
            return False

    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)

    @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 BindParameter(ColumnElement):
    """Represent a bound parameter value.

    """

    __visit_name__ = 'bindparam'

    _is_crud = False

    def __init__(self, key, value=NO_ARG, type_=None,
                            unique=False, required=NO_ARG,
                            quote=None, callable_=None,
                            isoutparam=False,
                            _compared_to_operator=None,
                            _compared_to_type=None):
        """Construct a new :class:`.BindParameter`.

            :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:`BindParameter` 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.

              Defaults to ``None``, however if neither ``value`` nor
              ``callable`` are passed explicitly, the ``required`` flag will be
              set to ``True`` which has the effect of requiring a value be present
              when the statement is actually executed.

              .. versionchanged:: 0.8 The ``required`` flag is set to ``True``
                 automatically if ``value`` or ``callable`` is not passed.

            :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:`BindParameter` at
              execution time.

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

            :param required:
              If ``True``, a value is required at execution time.  If not passed,
              is set to ``True`` or ``False`` based on whether or not
              one of ``value`` or ``callable`` were passed..

              .. versionchanged:: 0.8 If the ``required`` flag is not specified,
                 it will be set automatically to ``True`` or ``False`` depending
                 on whether or not the ``value`` or ``callable`` parameters
                 were specified.

            :param quote:
              True if this parameter name requires quoting and is not
              currently known as a SQLAlchemy reserved word; this currently
              only applies to the Oracle backend.

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

              .. seealso::

                :func:`.outparam`



        """
        if isinstance(key, ColumnClause):
            type_ = key.type
            key = key.name
        if required is NO_ARG:
            required = (value is NO_ARG and callable_ is None)
        if value is NO_ARG:
            value = None

        if quote is not None:
            key = quoted_name(key, quote)

        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 = type_api._type_map.get(type(value),
                        type_api.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:`BindParameter` to the given
        clause."""

        return isinstance(other, BindParameter) \
            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 'BindParameter(%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 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,)

    @property
    def selectable(self):
        return self

    _hide_froms = []

    def __init__(
                    self,
                    text='',
                    bind=None,
                    bindparams=None,
                    typemap=None,
                    autocommit=None):
        """Construct a new :class:`.TextClause` clause.

        E.g.::

            fom sqlalchemy import text

            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.

        """

        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:
                typemap[key] = type_api.to_instance(typemap[key])

        def repl(m):
            self.bindparams[m.group(1)] = BindParameter(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 type_api.NULLTYPE

    @property
    def comparator(self):
        return self.type.comparator_factory(self)

    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 list(self.bindparams.values())


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

    """

    __visit_name__ = 'null'

    def __init__(self):
        """Return a :class:`Null` object, which compiles to ``NULL``.

        """
        self.type = type_api.NULLTYPE

    def compare(self, other):
        return isinstance(other, Null)


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

    """

    __visit_name__ = 'false'

    def __init__(self):
        """Return a :class:`False_` object.

        """
        self.type = type_api.BOOLEANTYPE

    def compare(self, other):
        return isinstance(other, False_)

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

    """

    __visit_name__ = 'true'

    def __init__(self):
        """Return a :class:`True_` object.

        """
        self.type = type_api.BOOLEANTYPE

    def compare(self, other):
        return isinstance(other, True_)


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]

    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 = type_api.to_instance(kwargs.get('type_',
                type_api.BOOLEANTYPE))

    @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):
    """Represent a SQL tuple."""

    def __init__(self, *clauses, **kw):
        """Return a :class:`.Tuple`.

        Main usage is to produce a composite IN construct::

            from sqlalchemy import tuple_

            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.

        """

        clauses = [_literal_as_binds(c) for c in clauses]
        self.type = kw.pop('type_', None)
        if self.type is None:
            self.type = _type_from_args(clauses)
        super(Tuple, self).__init__(*clauses, **kw)

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

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


class Case(ColumnElement):
    """Represent a SQL ``CASE`` construct.


    """
    __visit_name__ = 'case'

    def __init__(self, whens, value=None, else_=None):
        """Produce a :class:`.Case` object.

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

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

        :param 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))

        """

        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()]))


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)



class Cast(ColumnElement):
    """Represent the SQL ``CAST`` construct."""

    __visit_name__ = 'cast'

    def __init__(self, clause, totype, **kwargs):
        """Return a :class:`.Cast` object.

        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)

        :class:`.Cast` is available using :func:`.cast` or alternatively
        ``func.cast`` from the :data:`.func` namespace.

        """
        self.type = type_api.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):
    """Represent a SQL EXTRACT clause, ``extract(field FROM expr)``."""

    __visit_name__ = 'extract'

    def __init__(self, field, expr, **kwargs):
        """Return a :class:`.Extract` construct.

        This is typically available as :func:`.extract`
        as well as ``func.extract`` from the
        :data:`.func` namespace.

        """
        self.type = type_api.INTEGERTYPE
        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):
    """Define a 'unary' expression.

    A unary expression has a single column expression
    and an operator.  The operator can be placed on the left
    (where it is called the 'operator') or right (where it is called the
    'modifier') of the column expression.

    """
    __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 = type_api.to_instance(type_)
        self.negate = negate

    @classmethod
    def _create_nullsfirst(cls, 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)


    @classmethod
    def _create_nullslast(cls, 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)


    @classmethod
    def _create_desc(cls, 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)

    @classmethod
    def _create_asc(cls, 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)

    @classmethod
    def _create_distinct(cls, 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)

    @util.memoized_property
    def _order_by_label_element(self):
        if self.modifier in (operators.desc_op, operators.asc_op):
            return self.element._order_by_label_element
        else:
            return None

    @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``.

    A :class:`.BinaryExpression` is generated automatically
    whenever two column expressions are used in a Python binary expresion::

        >>> from sqlalchemy.sql import column
        >>> column('a') + column('b')
        <sqlalchemy.sql.expression.BinaryExpression object at 0x101029dd0>
        >>> print column('a') + column('b')
        a + b

    """

    __visit_name__ = 'binary'

    def __init__(self, left, right, operator, type_=None,
                    negate=None, modifiers=None):
        # allow compatibility with libraries that
        # refer to BinaryExpression directly and pass strings
        if isinstance(operator, util.string_types):
            operator = operators.custom_op(operator)
        self._orig = (left, right)
        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 = type_api.to_instance(type_)
        self.negate = negate

        if modifiers is None:
            self.modifiers = {}
        else:
            self.modifiers = modifiers

    def __bool__(self):
        if self.operator in (operator.eq, operator.ne):
            return self.operator(hash(self._orig[0]), hash(self._orig[1]))
        else:
            raise TypeError("Boolean value of this clause is not defined")

    __nonzero__ = __bool__

    @property
    def is_comparison(self):
        return operators.is_comparison(self.operator)

    @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_=type_api.BOOLEANTYPE,
                modifiers=self.modifiers)
        else:
            return super(BinaryExpression, self)._negate()




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', type_api.NULLTYPE)

    @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']

    def compare(self, other, **kw):
        return isinstance(other, Grouping) and \
            self.element.compare(other.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):
        """Produce an :class:`.Over` object 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 :data:`~.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 :data:`~.expression.func`
        construct itself via the :meth:`.FunctionElement.over` method.

        .. versionadded:: 0.7

        """
        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.

    """

    __visit_name__ = 'label'

    def __init__(self, name, element, type_=None):
        """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
        :meth:`.ColumnElement.label` method on :class:`.ColumnElement`.

        :param name: label name

        :param obj: a :class:`.ColumnElement`.

        """
        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._proxies = [element]

    @util.memoized_property
    def _order_by_label_element(self):
        return self

    @util.memoized_property
    def type(self):
        return type_api.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, **kw):
        e = self.element._make_proxy(selectable,
                                name=name if name else self.name)
        e._proxies.append(self)
        if self._type is not None:
            e.type = self._type
        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.

    """
    __visit_name__ = 'column'

    onupdate = default = server_default = server_onupdate = None

    _memoized_property = util.group_expirable_memoized_property()

    def __init__(self, text, type_=None, is_literal=False, _selectable=None):
        """Construct a :class:`.ColumnClause` object.

        :param text: the text of the element.

        :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`.

        :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.


        """

        self.key = self.name = text
        self.table = _selectable
        self.type = type_api.to_instance(type_)
        self.is_literal = is_literal

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

    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):
        if util.py3k:
            return self.name
        else:
            return self.name.encode('ascii', 'backslashreplace')

    @_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

            # propagate name quoting rules for labels.
            if getattr(name, "quote", None) is not None:
                label = quoted_name(label, name.quote)
            elif getattr(t.name, "quote", None) is not None:
                label = quoted_name(label, t.name.quote)

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

    def _make_proxy(self, selectable, name=None, attach=True,
                            name_is_truncatable=False, **kw):
        # 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) if \
                                    name_is_truncatable else \
                                    (name or self.name),
                    type_=self.type,
                    _selectable=selectable,
                    is_literal=is_literal
                )
        if name is None:
            c.key = self.key
        c._proxies = [self]
        if selectable._is_clone_of is not None:
            c._is_clone_of = \
                selectable._is_clone_of.columns.get(c.key)

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


class _IdentifiedClause(Executable, ClauseElement):

    __visit_name__ = 'identified'
    _execution_options = \
        Executable._execution_options.union({'autocommit': False})

    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'


class quoted_name(util.text_type):
    """Represent a SQL identifier combined with quoting preferences.

    :class:`.quoted_name` is a Python unicode/str subclass which
    represents a particular identifier name along with a
    ``quote`` flag.  This ``quote`` flag, when set to
    ``True`` or ``False``, overrides automatic quoting behavior
    for this identifier in order to either unconditionally quote
    or to not quote the name.  If left at its default of ``None``,
    quoting behavior is applied to the identifier on a per-backend basis
    based on an examination of the token itself.

    A :class:`.quoted_name` object with ``quote=True`` is also
    prevented from being modified in the case of a so-called
    "name normalize" option.  Certain database backends, such as
    Oracle, Firebird, and DB2 "normalize" case-insensitive names
    as uppercase.  The SQLAlchemy dialects for these backends
    convert from SQLAlchemy's lower-case-means-insensitive convention
    to the upper-case-means-insensitive conventions of those backends.
    The ``quote=True`` flag here will prevent this conversion from occurring
    to support an identifier that's quoted as all lower case against
    such a backend.

    The :class:`.quoted_name` object is normally created automatically
    when specifying the name for key schema constructs such as :class:`.Table`,
    :class:`.Column`, and others.   The class can also be passed explicitly
    as the name to any function that receives a name which can be quoted.
    Such as to use the :meth:`.Engine.has_table` method with an unconditionally
    quoted name::

        from sqlaclchemy import create_engine
        from sqlalchemy.sql.elements import quoted_name

        engine = create_engine("oracle+cx_oracle://some_dsn")
        engine.has_table(quoted_name("some_table", True))

    The above logic will run the "has table" logic against the Oracle backend,
    passing the name exactly as ``"some_table"`` without converting to
    upper case.

    .. versionadded:: 0.9.0

    """

    def __new__(cls, value, quote):
        if value is None:
            return None
        elif isinstance(value, cls) and (
                quote is None or value.quote == quote
            ):
            return value
        self = super(quoted_name, cls).__new__(cls, value)
        self.quote = quote
        return self

    def __reduce__(self):
        return quoted_name, (util.text_type(self), self.quote)

    @util.memoized_instancemethod
    def lower(self):
        if self.quote:
            return self
        else:
            return util.text_type(self).lower()

    @util.memoized_instancemethod
    def upper(self):
        if self.quote:
            return self
        else:
            return util.text_type(self).upper()

    def __repr__(self):
        return "'%s'" % self

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

    def __new__(cls, value, quote=None):
        quote = getattr(value, "quote", quote)
        return super(_truncated_label, cls).__new__(cls, value, quote)

    def __reduce__(self):
        return self.__class__, (util.text_type(self), self.quote)

    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(
                    quoted_name(
                        util.text_type.__add__(self, util.text_type(other)),
                        self.quote)
                )

    def __radd__(self, other):
        return _anonymous_label(
                    quoted_name(
                        util.text_type.__add__(util.text_type(other), self),
                        self.quote)
                    )

    def apply_map(self, map_):
        if self.quote is not None:
            # preserve quoting only if necessary
            return quoted_name(self % map_, self.quote)
        else:
            # else skip the constructor call
            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, util.string_types):
        return element
    else:
        try:
            return str(element)
        except:
            return "unprintable element %r" % element


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 _cloned_difference(a, b):
    all_overlap = set(_expand_cloned(a)).intersection(_expand_cloned(b))
    return set(elem for elem in a
                if not all_overlap.intersection(elem._cloned_set))


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


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

    return isinstance(col, ColumnElement)


def _find_columns(clause):
    """locate Column objects within the given expression."""

    cols = util.column_set()
    traverse(clause, {}, {'column': cols.add})
    return cols


# there is some inconsistency here between the usage of
# inspect() vs. checking for Visitable and __clause_element__.
# Ideally all functions here would derive from inspect(),
# however the inspect() versions add significant callcount
# overhead for critical functions like _interpret_as_column_or_from().
# Generally, the column-based functions are more performance critical
# and are fine just checking for __clause_element__().  it's only
# _interpret_as_from() where we'd like to be able to receive ORM entities
# that have no defined namespace, hence inspect() is needed there.


def _column_as_key(element):
    if isinstance(element, util.string_types):
        return element
    if hasattr(element, '__clause_element__'):
        element = element.__clause_element__()
    try:
        return element.key
    except AttributeError:
        return None


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


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


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 _is_literal(element):
    return not isinstance(element, Visitable) and \
            not hasattr(element, '__clause_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 _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 BindParameter(name, element, type_=type_, unique=True)
    else:
        return element


def _interpret_as_column_or_from(element):
    if isinstance(element, Visitable):
        return element
    elif hasattr(element, '__clause_element__'):
        return element.__clause_element__()

    insp = inspection.inspect(element, raiseerr=False)
    if insp is None:
        if isinstance(element, (util.NoneType, bool)):
            return _const_expr(element)
    elif hasattr(insp, "selectable"):
        return insp.selectable

    return ColumnClause(str(element), is_literal=True)


def _const_expr(element):
    if isinstance(element, (Null, False_, True_)):
        return element
    elif 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 _type_from_args(args):
    for a in args:
        if not a.type._isnull:
            return a.type
    else:
        return type_api.NULLTYPE


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


class AnnotatedColumnElement(Annotated):
    def __init__(self, element, values):
        Annotated.__init__(self, element, values)
        ColumnElement.comparator._reset(self)
        for attr in ('name', 'key'):
            if self.__dict__.get(attr, False) is None:
                self.__dict__.pop(attr)

    def _with_annotations(self, values):
        clone = super(AnnotatedColumnElement, self)._with_annotations(values)
        ColumnElement.comparator._reset(clone)
        return clone

    @util.memoized_property
    def name(self):
        """pull 'name' from parent, if not present"""
        return self._Annotated__element.name

    @util.memoized_property
    def key(self):
        """pull 'key' from parent, if not present"""
        return self._Annotated__element.key

    @util.memoized_property
    def info(self):
        return self._Annotated__element.info