aboutsummaryrefslogtreecommitdiff
path: root/doc/src/sgml/datatype.sgml
blob: 2689349b8f50166bf6abfd1f25bcade293b4eb58 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
<!--
$PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.142 2004/02/01 06:55:07 tgl Exp $
-->

 <chapter id="datatype">
  <title id="datatype-title">Data Types</title>

  <indexterm zone="datatype">
   <primary>data type</primary>
  </indexterm>

  <indexterm>
   <primary>type</primary>
   <see>data type</see>
  </indexterm>

  <para>
   <productname>PostgreSQL</productname> has a rich set of native data 
   types available to users.
   Users may add new types to <productname>PostgreSQL</productname> using the
   <command>CREATE TYPE</command> command.
  </para>

  <para>
   <xref linkend="datatype-table"> shows all built-in general-purpose data types.
   Most of the alternative names
   listed in the 
   <quote>Aliases</quote> column are the names used internally by
   <productname>PostgreSQL</productname> for historical reasons.  In
   addition, some internally used or deprecated types are available,
   but they are not listed here.
  </para>

   <table id="datatype-table">
    <title>Data Types</title>
    <tgroup cols="3">
     <thead>
      <row>
       <entry>Name</entry>
       <entry>Aliases</entry>
       <entry>Description</entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry><type>bigint</type></entry>
       <entry><type>int8</type></entry>
       <entry>signed eight-byte integer</entry>
      </row>

      <row>
       <entry><type>bigserial</type></entry>
       <entry><type>serial8</type></entry>
       <entry>autoincrementing eight-byte integer</entry>
      </row>

      <row>
       <entry><type>bit</type></entry>
       <entry></entry>
       <entry>fixed-length bit string</entry>
      </row>

      <row>
       <entry><type>bit varying(<replaceable>n</replaceable>)</type></entry>
       <entry><type>varbit(<replaceable>n</replaceable>)</type></entry>
       <entry>variable-length bit string</entry>
      </row>

      <row>
       <entry><type>boolean</type></entry>
       <entry><type>bool</type></entry>
       <entry>logical Boolean (true/false)</entry>
      </row>

      <row>
       <entry><type>box</type></entry>
       <entry></entry>
       <entry>rectangular box in the plane</entry>
      </row>

      <row>
       <entry><type>bytea</type></entry>
       <entry></entry>
       <entry>binary data</entry>
      </row>

      <row>
       <entry><type>character varying(<replaceable>n</replaceable>)</type></entry>
       <entry><type>varchar(<replaceable>n</replaceable>)</type></entry>
       <entry>variable-length character string</entry>
      </row>

      <row>
       <entry><type>character(<replaceable>n</replaceable>)</type></entry>
       <entry><type>char(<replaceable>n</replaceable>)</type></entry>
       <entry>fixed-length character string</entry>
      </row>

      <row>
       <entry><type>cidr</type></entry>
       <entry></entry>
       <entry>IPv4 or IPv6 network address</entry>
      </row>

      <row>
       <entry><type>circle</type></entry>
       <entry></entry>
       <entry>circle in the plane</entry>
      </row>

      <row>
       <entry><type>date</type></entry>
       <entry></entry>
       <entry>calendar date (year, month, day)</entry>
      </row>

      <row>
       <entry><type>double precision</type></entry>
       <entry><type>float8</type></entry>
       <entry>double precision floating-point number</entry>
      </row>

      <row>
       <entry><type>inet</type></entry>
       <entry></entry>
       <entry>IPv4 or IPv6 host address</entry>
      </row>

      <row>
       <entry><type>integer</type></entry>
       <entry><type>int</type>, <type>int4</type></entry>
       <entry>signed four-byte integer</entry>
      </row>

      <row>
       <entry><type>interval(<replaceable>p</replaceable>)</type></entry>
       <entry></entry>
       <entry>time span</entry>
      </row>

      <row>
       <entry><type>line</type></entry>
       <entry></entry>
       <entry>infinite line in the plane (not fully implemented)</entry>
      </row>

      <row>
       <entry><type>lseg</type></entry>
       <entry></entry>
       <entry>line segment in the plane</entry>
      </row>

      <row>
       <entry><type>macaddr</type></entry>
       <entry></entry>
       <entry>MAC address</entry>
      </row>

      <row>
       <entry><type>money</type></entry>
       <entry></entry>
       <entry>currency amount</entry>
      </row>

      <row>
       <entry><type>numeric [ (<replaceable>p</replaceable>,
         <replaceable>s</replaceable>) ]</type></entry>
       <entry><type>decimal [ (<replaceable>p</replaceable>,
         <replaceable>s</replaceable>) ]</type></entry>
       <entry>exact numeric with selectable precision</entry>
      </row>

      <row>
       <entry><type>path</type></entry>
       <entry></entry>
       <entry>open and closed geometric path in the plane</entry>
      </row>

      <row>
       <entry><type>point</type></entry>
       <entry></entry>
       <entry>geometric point in the plane</entry>
      </row>

      <row>
       <entry><type>polygon</type></entry>
       <entry></entry>
       <entry>closed geometric path in the plane</entry>
      </row>

      <row>
       <entry><type>real</type></entry>
       <entry><type>float4</type></entry>
       <entry>single precision floating-point number</entry>
      </row>

      <row>
       <entry><type>smallint</type></entry>
       <entry><type>int2</type></entry>
       <entry>signed two-byte integer</entry>
      </row>

      <row>
       <entry><type>serial</type></entry>
       <entry><type>serial4</type></entry>
       <entry>autoincrementing four-byte integer</entry>
      </row>

      <row>
       <entry><type>text</type></entry>
       <entry></entry>
       <entry>variable-length character string</entry>
      </row>

      <row>
       <entry><type>time [ (<replaceable>p</replaceable>) ] [ without time zone ]</type></entry>
       <entry></entry>
       <entry>time of day</entry>
      </row>

      <row>
       <entry><type>time [ (<replaceable>p</replaceable>) ] with time zone</type></entry>
       <entry><type>timetz</type></entry>
       <entry>time of day, including time zone</entry>
      </row>

      <row>
       <entry><type>timestamp [ (<replaceable>p</replaceable>) ] without time zone</type></entry>
       <entry><type>timestamp</type></entry>
       <entry>date and time</entry>
      </row>

      <row>
       <entry><type>timestamp [ (<replaceable>p</replaceable>) ] [ with time zone ]</type></entry>
       <entry><type>timestamptz</type></entry>
       <entry>date and time, including time zone</entry>
      </row>
     </tbody>
    </tgroup>
   </table>

  <note>
   <title>Compatibility</title>
   <para>
    The following types (or spellings thereof) are specified by
    <acronym>SQL</acronym>: <type>bit</type>, <type>bit
    varying</type>, <type>boolean</type>, <type>char</type>,
    <type>character varying</type>, <type>character</type>,
    <type>varchar</type>, <type>date</type>, <type>double
    precision</type>, <type>integer</type>, <type>interval</type>,
    <type>numeric</type>, <type>decimal</type>, <type>real</type>,
    <type>smallint</type>, <type>time</type> (with or without time zone),
    <type>timestamp</type> (with or without time zone).
   </para>
  </note>

  <para>
   Each data type has an external representation determined by its input
   and output functions.  Many of the built-in types have
   obvious external formats.  However, several types are either unique
   to <productname>PostgreSQL</productname>, such as open and closed
   paths, or have several possibilities for formats, such as the date
   and time types.
   Some of the input and output functions are not invertible.  That is,
   the result of an output function may lose accuracy when compared to
   the original input.
  </para>

  <para>
   Some of the operators and functions (e.g.,
   addition and multiplication) do not perform run-time error-checking in the
   interests of improving execution speed.
   On some systems, for example, the numeric operators for some data types may
   silently cause underflow or overflow.
  </para>

  <sect1 id="datatype-numeric">
   <title>Numeric Types</title>

   <indexterm zone="datatype-numeric">
    <primary>data type</primary>
    <secondary>numeric</secondary>
   </indexterm>

   <para>
    Numeric types consist of two-, four-, and eight-byte integers,
    four- and eight-byte floating-point numbers, and fixed-precision
    decimals.  <xref linkend="datatype-numeric-table"> lists the
    available types.
   </para>

    <table id="datatype-numeric-table">
     <title>Numeric Types</title>
     <tgroup cols="4">
      <thead>
       <row>
        <entry>Name</entry>
        <entry>Storage Size</entry>
        <entry>Description</entry>
        <entry>Range</entry>
       </row>
      </thead>

      <tbody>
       <row>
        <entry><type>smallint</></entry>
        <entry>2 bytes</entry>
        <entry>small-range integer</entry>
        <entry>-32768 to +32767</entry>
       </row>
       <row>
        <entry><type>integer</></entry>
        <entry>4 bytes</entry>
        <entry>usual choice for integer</entry>
        <entry>-2147483648 to +2147483647</entry>
       </row>
       <row>
        <entry><type>bigint</></entry>
        <entry>8 bytes</entry>
        <entry>large-range integer</entry>
        <entry>-9223372036854775808 to 9223372036854775807</entry>
       </row>

       <row>
        <entry><type>decimal</></entry>
        <entry>variable</entry>
        <entry>user-specified precision, exact</entry>
        <entry>no limit</entry>
       </row>
       <row>
        <entry><type>numeric</></entry>
        <entry>variable</entry>
        <entry>user-specified precision, exact</entry>
        <entry>no limit</entry>
       </row>

       <row>
        <entry><type>real</></entry>
        <entry>4 bytes</entry>
        <entry>variable-precision, inexact</entry>
        <entry>6 decimal digits precision</entry>
       </row>
       <row>
        <entry><type>double precision</></entry>
        <entry>8 bytes</entry>
        <entry>variable-precision, inexact</entry>
        <entry>15 decimal digits precision</entry>
       </row>

       <row>
        <entry><type>serial</></entry>
        <entry>4 bytes</entry>
        <entry>autoincrementing integer</entry>
        <entry>1 to 2147483647</entry>
       </row>

       <row>
        <entry><type>bigserial</type></entry>
        <entry>8 bytes</entry>
        <entry>large autoincrementing integer</entry>
        <entry>1 to 9223372036854775807</entry>
       </row>
      </tbody>
     </tgroup>
    </table>

   <para>
    The syntax of constants for the numeric types is described in
    <xref linkend="sql-syntax-constants">.  The numeric types have a
    full set of corresponding arithmetic operators and
    functions. Refer to <xref linkend="functions"> for more
    information.  The following sections describe the types in detail.
   </para>

   <sect2 id="datatype-int">
    <title>Integer Types</title>

    <indexterm zone="datatype-int">
     <primary>integer</primary>
    </indexterm>

    <indexterm zone="datatype-int">
     <primary>smallint</primary>
    </indexterm>

    <indexterm zone="datatype-int">
     <primary>bigint</primary>
    </indexterm>

    <indexterm>
     <primary>int4</primary>
     <see>integer</see>
    </indexterm>

    <indexterm>
     <primary>int2</primary>
     <see>smallint</see>
    </indexterm>

    <indexterm>
     <primary>int8</primary>
     <see>bigint</see>
    </indexterm>

    <para>
     The types <type>smallint</type>, <type>integer</type>, and
     <type>bigint</type> store whole numbers, that is, numbers without
     fractional components, of various ranges.  Attempts to store
     values outside of the allowed range will result in an error.
    </para>

    <para>
     The type <type>integer</type> is the usual choice, as it offers
     the best balance between range, storage size, and performance.
     The <type>smallint</type> type is generally only used if disk
     space is at a premium.  The <type>bigint</type> type should only
     be used if the <type>integer</type> range is not sufficient,
     because the latter is definitely faster.
    </para>

    <para>
     The <type>bigint</type> type may not function correctly on all
     platforms, since it relies on compiler support for eight-byte
     integers.  On a machine without such support, <type>bigint</type>
     acts the same as <type>integer</type> (but still takes up eight
     bytes of storage).  However, we are not aware of any reasonable
     platform where this is actually the case.
    </para>

    <para>
     <acronym>SQL</acronym> only specifies the integer types
     <type>integer</type> (or <type>int</type>) and
     <type>smallint</type>.  The type <type>bigint</type>, and the
     type names <type>int2</type>, <type>int4</type>, and
     <type>int8</type> are extensions, which are shared with various
     other <acronym>SQL</acronym> database systems.
    </para>

   </sect2>

   <sect2 id="datatype-numeric-decimal">
    <title>Arbitrary Precision Numbers</title>

    <indexterm zone="datatype-numeric-decimal">
     <primary>numeric (data type)</primary>
    </indexterm>

    <indexterm>
     <primary>decimal</primary>
     <see>numeric</see>
    </indexterm>

    <para>
     The type <type>numeric</type> can store numbers with up to 1000
     digits of precision and perform calculations exactly. It is
     especially recommended for storing monetary amounts and other
     quantities where exactness is required. However, the
     <type>numeric</type> type is very slow compared to the
     floating-point types described in the next section.
    </para>

    <para>
     In what follows we use these terms:  The
     <firstterm>scale</firstterm> of a <type>numeric</type> is the
     count of decimal digits in the fractional part, to the right of
     the decimal point.  The <firstterm>precision</firstterm> of a
     <type>numeric</type> is the total count of significant digits in
     the whole number, that is, the number of digits to both sides of
     the decimal point.  So the number 23.5141 has a precision of 6
     and a scale of 4.  Integers can be considered to have a scale of
     zero.
    </para>

    <para>
     Both the precision and the scale of the numeric type can be
     configured.  To declare a column of type <type>numeric</type> use
     the syntax
<programlisting>
NUMERIC(<replaceable>precision</replaceable>, <replaceable>scale</replaceable>)
</programlisting>
     The precision must be positive, the scale zero or positive.
     Alternatively,
<programlisting>
NUMERIC(<replaceable>precision</replaceable>)
</programlisting>
     selects a scale of 0.  Specifying
<programlisting>
NUMERIC
</programlisting>
     without any precision or scale creates a column in which numeric
     values of any precision and scale can be stored, up to the
     implementation limit on precision.  A column of this kind will
     not coerce input values to any particular scale, whereas
     <type>numeric</type> columns with a declared scale will coerce
     input values to that scale.  (The <acronym>SQL</acronym> standard
     requires a default scale of 0, i.e., coercion to integer
     precision.  We find this a bit useless.  If you're concerned
     about portability, always specify the precision and scale
     explicitly.)
    </para>

    <para>
     If the precision or scale of a value is greater than the declared
     precision or scale of a column, the system will attempt to round
     the value.  If the value cannot be rounded so as to satisfy the
     declared limits, an error is raised.
    </para>

    <para>
     The types <type>decimal</type> and <type>numeric</type> are
     equivalent.  Both types are part of the <acronym>SQL</acronym>
     standard.
    </para>
   </sect2>


   <sect2 id="datatype-float">
    <title>Floating-Point Types</title>

    <indexterm zone="datatype-float">
     <primary>real</primary>
    </indexterm>

    <indexterm zone="datatype-float">
     <primary>double precision</primary>
    </indexterm>

    <indexterm>
     <primary>float4</primary>
     <see>real</see>
    </indexterm>

    <indexterm>
     <primary>float8</primary>
     <see>double precision</see>
    </indexterm>

    <indexterm zone="datatype-float">
     <primary>floating point</primary>
    </indexterm>

    <para>
     The data types <type>real</type> and <type>double
     precision</type> are inexact, variable-precision numeric types.
     In practice, these types are usually implementations of
     <acronym>IEEE</acronym> Standard 754 for Binary Floating-Point
     Arithmetic (single and double precision, respectively), to the
     extent that the underlying processor, operating system, and
     compiler support it.
    </para>

    <para>
     Inexact means that some values cannot be converted exactly to the
     internal format and are stored as approximations, so that storing
     and printing back out a value may show slight discrepancies.
     Managing these errors and how they propagate through calculations
     is the subject of an entire branch of mathematics and computer
     science and will not be discussed further here, except for the
     following points:
     <itemizedlist>
      <listitem>
       <para>
        If you require exact storage and calculations (such as for
        monetary amounts), use the <type>numeric</type> type instead.
       </para>
      </listitem>

      <listitem>
       <para>
        If you want to do complicated calculations with these types
        for anything important, especially if you rely on certain
        behavior in boundary cases (infinity, underflow), you should
        evaluate the implementation carefully.
       </para>
      </listitem>

      <listitem>
       <para>
        Comparing two floating-point values for equality may or may
        not work as expected.
       </para>
      </listitem>
     </itemizedlist>
    </para>

    <para>
     On most platforms, the <type>real</type> type has a range of at least
     1E-37 to 1E+37 with a precision of at least 6 decimal digits.  The
     <type>double precision</type> type typically has a range of around
     1E-307 to 1E+308 with a precision of at least 15 digits.  Values that
     are too large or too small will cause an error.  Rounding may
     take place if the precision of an input number is too high.
     Numbers too close to zero that are not representable as distinct
     from zero will cause an underflow error.
    </para>

    <para>
     <productname>PostgreSQL</productname> also supports the SQL-standard
     notations <type>float</type> and
     <type>float(<replaceable>p</replaceable>)</type> for specifying
     inexact numeric types.  Here, <replaceable>p</replaceable> specifies
     the minimum acceptable precision in binary digits.
     <productname>PostgreSQL</productname> accepts 
     <type>float(1)</type> to <type>float(24)</type> as selecting the
     <type>real</type> type, while 
     <type>float(25)</type> to <type>float(53)</type> select
     <type>double precision</type>.  Values of <replaceable>p</replaceable>
     outside the allowed range draw an error.
     <type>float</type> with no precision specified is taken to mean
     <type>double precision</type>.
    </para>

    <note>
     <para>
      Prior to <productname>PostgreSQL</productname> 7.4, the precision in
      <type>float(<replaceable>p</replaceable>)</type> was taken to mean
      so many decimal digits.  This has been corrected to match the SQL
      standard, which specifies that the precision is measured in binary
      digits.  The assumption that <type>real</type> and
      <type>double precision</type> have exactly 24 and 53 bits in the
      mantissa respectively is correct for IEEE-standard floating point
      implementations.  On non-IEEE platforms it may be off a little, but
      for simplicity the same ranges of <replaceable>p</replaceable> are used
      on all platforms.
     </para>
    </note>

   </sect2>

   <sect2 id="datatype-serial">
    <title>Serial Types</title>

    <indexterm zone="datatype-serial">
     <primary>serial</primary>
    </indexterm>

    <indexterm zone="datatype-serial">
     <primary>bigserial</primary>
    </indexterm>

    <indexterm zone="datatype-serial">
     <primary>serial4</primary>
    </indexterm>

    <indexterm zone="datatype-serial">
     <primary>serial8</primary>
    </indexterm>

    <indexterm>
     <primary>auto-increment</primary>
     <see>serial</see>
    </indexterm>

    <indexterm>
     <primary>sequence</primary>
     <secondary>and serial type</secondary>
    </indexterm>

    <para>
     The data types <type>serial</type> and <type>bigserial</type>
     are not true types, but merely
     a notational convenience for setting up unique identifier columns
     (similar to the <literal>AUTO_INCREMENT</literal> property
     supported by some other databases). In the current
     implementation, specifying

<programlisting>
CREATE TABLE <replaceable class="parameter">tablename</replaceable> (
    <replaceable class="parameter">colname</replaceable> SERIAL
);
</programlisting>

     is equivalent to specifying:

<programlisting>
CREATE SEQUENCE <replaceable class="parameter">tablename</replaceable>_<replaceable class="parameter">colname</replaceable>_seq;
CREATE TABLE <replaceable class="parameter">tablename</replaceable> (
    <replaceable class="parameter">colname</replaceable> integer DEFAULT nextval('<replaceable class="parameter">tablename</replaceable>_<replaceable class="parameter">colname</replaceable>_seq') NOT NULL
);
</programlisting>

     Thus, we have created an integer column and arranged for its default
     values to be assigned from a sequence generator.  A <literal>NOT NULL</>
     constraint is applied to ensure that a null value cannot be explicitly
     inserted, either.  In most cases you would also want to attach a
     <literal>UNIQUE</> or <literal>PRIMARY KEY</> constraint to prevent
     duplicate values from being inserted by accident, but this is
     not automatic.
    </para>

    <note>
     <para>
      Prior to <productname>PostgreSQL</productname> 7.3, <type>serial</type>
      implied <literal>UNIQUE</literal>.  This is no longer automatic.  If
      you wish a serial column to be in a unique constraint or a 
      primary key, it must now be specified, same as with
      any other data type.
     </para>
    </note>

    <para>
     To insert the next value of the sequence into the <type>serial</type>
     column, specify that the <type>serial</type>
     column should be assigned its default value. This can be done
     either by excluding the column from the list of columns in
     the <command>INSERT</command> statement, or through the use of
     the <literal>DEFAULT</literal> key word.
    </para>

    <para>
     The type names <type>serial</type> and <type>serial4</type> are
     equivalent: both create <type>integer</type> columns.  The type
     names <type>bigserial</type> and <type>serial8</type> work just
     the same way, except that they create a <type>bigint</type>
     column.  <type>bigserial</type> should be used if you anticipate
     the use of more than 2<superscript>31</> identifiers over the
     lifetime of the table.
    </para>

    <para>
     The sequence created for a <type>serial</type> column is
     automatically dropped when the owning column is dropped, and
     cannot be dropped otherwise.  (This was not true in
     <productname>PostgreSQL</productname> releases before 7.3.  Note
     that this automatic drop linkage will not occur for a sequence
     created by reloading a dump from a pre-7.3 database; the dump
     file does not contain the information needed to establish the
     dependency link.) Furthermore, this dependency between sequence
     and column is made only for the <type>serial</> column itself; if
     any other columns reference the sequence (perhaps by manually
     calling the <function>nextval</> function), they will be broken
     if the sequence is removed. Using a <type>serial</> column's sequence
     in such a fashion is considered bad form; if you wish to feed several
     columns from the same sequence generator, create the sequence as an
     independent object.
    </para>
   </sect2>
  </sect1>

  <sect1 id="datatype-money">
   <title>Monetary Types</title>

   <note>
    <para>
     The <type>money</type> type is deprecated. Use
     <type>numeric</type> or <type>decimal</type> instead, in
     combination with the <function>to_char</function> function.
    </para>
   </note>

   <para>
    The <type>money</type> type stores a currency amount with a fixed
    fractional precision; see <xref
    linkend="datatype-money-table">.
    Input is accepted in a variety of formats, including integer and
    floating-point literals, as well as <quote>typical</quote>
    currency formatting, such as <literal>'$1,000.00'</literal>.
    Output is generally in the latter form but depends on the locale.
   </para>

    <table id="datatype-money-table">
     <title>Monetary Types</title>
     <tgroup cols="4">
      <thead>
       <row>
        <entry>Name</entry>
        <entry>Storage Size</entry>
        <entry>Description</entry>
        <entry>Range</entry>
       </row>
      </thead>
      <tbody>
       <row>
        <entry>money</entry>
        <entry>4 bytes</entry>
        <entry>currency amount</entry>
        <entry>-21474836.48 to +21474836.47</entry>
       </row>
      </tbody>
     </tgroup>
    </table>
  </sect1>


  <sect1 id="datatype-character">
   <title>Character Types</title>

   <indexterm zone="datatype-character">
    <primary>character string</primary>
    <secondary>data types</secondary>
   </indexterm>

   <indexterm>
    <primary>string</primary>
    <see>character string</see>
   </indexterm>

   <indexterm zone="datatype-character">
    <primary>character</primary>
   </indexterm>

   <indexterm zone="datatype-character">
    <primary>character varying</primary>
   </indexterm>

   <indexterm zone="datatype-character">
    <primary>text</primary>
   </indexterm>

   <indexterm zone="datatype-character">
    <primary>char</primary>
   </indexterm>

   <indexterm zone="datatype-character">
    <primary>varchar</primary>
   </indexterm>

    <table id="datatype-character-table">
     <title>Character Types</title>
     <tgroup cols="2">
      <thead>
       <row>
        <entry>Name</entry>
        <entry>Description</entry>
       </row>
      </thead>
      <tbody>
       <row>
        <entry><type>character varying(<replaceable>n</>)</type>, <type>varchar(<replaceable>n</>)</type></entry>
        <entry>variable-length with limit</entry>
       </row>
       <row>
        <entry><type>character(<replaceable>n</>)</type>, <type>char(<replaceable>n</>)</type></entry>
        <entry>fixed-length, blank padded</entry>
       </row>
       <row>
        <entry><type>text</type></entry>
        <entry>variable unlimited length</entry>
       </row>
     </tbody>
     </tgroup>
    </table>

   <para>
    <xref linkend="datatype-character-table"> shows the
    general-purpose character types available in
    <productname>PostgreSQL</productname>.
   </para>

   <para>
    <acronym>SQL</acronym> defines two primary character types:
    <type>character varying(<replaceable>n</>)</type> and
    <type>character(<replaceable>n</>)</type>, where <replaceable>n</>
    is a positive integer.  Both of these types can store strings up to
    <replaceable>n</> characters in length.  An attempt to store a
    longer string into a column of these types will result in an
    error, unless the excess characters are all spaces, in which case
    the string will be truncated to the maximum length. (This somewhat
    bizarre exception is required by the <acronym>SQL</acronym>
    standard.) If the string to be stored is shorter than the declared
    length, values of type <type>character</type> will be space-padded;
    values of type <type>character varying</type> will simply store the
    shorter
    string.
   </para>

    <para>
     If one explicitly casts a value to <type>character
     varying(<replaceable>n</>)</type> or
     <type>character(<replaceable>n</>)</type>, then an over-length
     value will be truncated to <replaceable>n</> characters without
     raising an error. (This too is required by the
     <acronym>SQL</acronym> standard.)
    </para>

   <note>
    <para>
     Prior to <productname>PostgreSQL</> 7.2, strings that were too long were
     always truncated without raising an error, in either explicit or
     implicit casting contexts.
    </para>
   </note>

   <para>
    The notations <type>varchar(<replaceable>n</>)</type> and
    <type>char(<replaceable>n</>)</type> are aliases for <type>character
    varying(<replaceable>n</>)</type> and
    <type>character(<replaceable>n</>)</type>, respectively.
    <type>character</type> without length specifier is equivalent to
    <type>character(1)</type>; if <type>character varying</type> is used
    without length specifier, the type accepts strings of any size. The
    latter is a <productname>PostgreSQL</> extension.
   </para>

   <para>
    In addition, <productname>PostgreSQL</productname> provides the
    <type>text</type> type, which stores strings of any length.
    Although the type <type>text</type> is not in the
    <acronym>SQL</acronym> standard, several other SQL database
    management systems have it as well.
   </para>

   <para>
    Values of type <type>character</type> are physically padded
    with spaces to the specified width <replaceable>n</>, and are
    stored and displayed that way.  However, the padding spaces are
    treated as semantically insignificant.  Trailing spaces are
    disregarded when comparing two values of type <type>character</type>,
    and they will be removed when converting a <type>character</type> value
    to one of the other string types.  Note that trailing spaces
    <emphasis>are</> semantically significant in
    <type>character varying</type> and <type>text</type> values.
   </para>

   <para>
    The storage requirement for data of these types is 4 bytes plus the
    actual string, and in case of <type>character</type> plus the
    padding. Long strings are compressed by the system automatically, so
    the physical requirement on disk may be less. Long values are also
    stored in background tables so they do not interfere with rapid
    access to the shorter column values. In any case, the longest
    possible character string that can be stored is about 1 GB. (The
    maximum value that will be allowed for <replaceable>n</> in the data
    type declaration is less than that. It wouldn't be very useful to
    change this because with multibyte character encodings the number of
    characters and bytes can be quite different anyway. If you desire to
    store long strings with no specific upper limit, use
    <type>text</type> or <type>character varying</type> without a length
    specifier, rather than making up an arbitrary length limit.)
   </para>

   <tip>
    <para>
     There are no performance differences between these three types,
     apart from the increased storage size when using the blank-padded
     type.  While <type>character(<replaceable>n</>)</type> has performance
     advantages in some other database systems, it has no such advantages in
     <productname>PostgreSQL</productname>.  In most situations
     <type>text</type> or <type>character varying</type> should be used
     instead.
    </para>
   </tip>

   <para>
    Refer to <xref linkend="sql-syntax-strings"> for information about
    the syntax of string literals, and to <xref linkend="functions">
    for information about available operators and functions.
   </para>

   <example>
    <title>Using the character types</title>

<programlisting>
CREATE TABLE test1 (a character(4));
INSERT INTO test1 VALUES ('ok');
SELECT a, char_length(a) FROM test1; -- <co id="co.datatype-char">
<computeroutput>
  a   | char_length
------+-------------
 ok   |           2
</computeroutput>

CREATE TABLE test2 (b varchar(5));
INSERT INTO test2 VALUES ('ok');
INSERT INTO test2 VALUES ('good      ');
INSERT INTO test2 VALUES ('too long');
<computeroutput>ERROR:  value too long for type character varying(5)</computeroutput>
INSERT INTO test2 VALUES ('too long'::varchar(5)); -- explicit truncation
SELECT b, char_length(b) FROM test2;
<computeroutput>
   b   | char_length
-------+-------------
 ok    |           2
 good  |           5
 too l |           5
</computeroutput>
</programlisting>
    <calloutlist>
     <callout arearefs="co.datatype-char">
      <para>
       The <function>char_length</function> function is discussed in
       <xref linkend="functions-string">.
      </para>
     </callout>
    </calloutlist>
   </example>

   <para>
    There are two other fixed-length character types in
    <productname>PostgreSQL</productname>, shown in <xref
    linkend="datatype-character-special-table">. The <type>name</type>
    type exists <emphasis>only</emphasis> for storage of identifiers
    in the internal system catalogs and is not intended for use by the general user. Its
    length is currently defined as 64 bytes (63 usable characters plus
    terminator) but should be referenced using the constant
    <symbol>NAMEDATALEN</symbol>. The length is set at compile time (and
    is therefore adjustable for special uses); the default maximum
    length may change in a future release. The type <type>"char"</type>
    (note the quotes) is different from <type>char(1)</type> in that it
    only uses one byte of storage. It is internally used in the system
    catalogs as a poor-man's enumeration type.
   </para>

    <table id="datatype-character-special-table">
     <title>Special Character Types</title>
     <tgroup cols="3">
      <thead>
       <row>
        <entry>Name</entry>
        <entry>Storage Size</entry>
        <entry>Description</entry>
       </row>
      </thead>
      <tbody>
       <row>
        <entry><type>"char"</type></entry>
        <entry>1 byte</entry>
        <entry>single-character internal type</entry>
       </row>
       <row>
        <entry><type>name</type></entry>
        <entry>64 bytes</entry>
        <entry>internal type for object names</entry>
       </row>
      </tbody>
     </tgroup>
    </table>

  </sect1>

 <sect1 id="datatype-binary">
  <title>Binary Data Types</title>

  <indexterm zone="datatype-binary">
   <primary>binary data</primary>
  </indexterm>

  <indexterm zone="datatype-binary">
   <primary>bytea</primary>
  </indexterm>

   <para>
    The <type>bytea</type> data type allows storage of binary strings;
    see <xref linkend="datatype-binary-table">.
   </para>

   <table id="datatype-binary-table">
    <title>Binary Data Types</title>
    <tgroup cols="3">
     <thead>
      <row>
       <entry>Name</entry>
       <entry>Storage Size</entry>
       <entry>Description</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry><type>bytea</type></entry>
       <entry>4 bytes plus the actual binary string</entry>
       <entry>variable-length binary string</entry>
      </row>
     </tbody>
    </tgroup>
   </table>

   <para>
    A binary string is a sequence of octets (or bytes).  Binary
    strings are distinguished from characters strings by two
    characteristics: First, binary strings specifically allow storing
    octets of value zero and other <quote>non-printable</quote>
    octets (defined as octets outside the range 32 to 126).
    Second, operations on binary strings process the actual bytes,
    whereas the encoding and processing of character strings depends
    on locale settings.
   </para>

   <para>
    When entering <type>bytea</type> values, octets of certain values
    <emphasis>must</emphasis> be escaped (but all octet values
    <emphasis>may</emphasis> be escaped) when used as part of a string
    literal in an <acronym>SQL</acronym> statement. In general, to
    escape an octet, it is converted into the three-digit octal number
    equivalent of its decimal octet value, and preceded by two
    backslashes. <xref linkend="datatype-binary-sqlesc"> contains the
    characters which must be escaped, and gives the alternate escape
    sequences where applicable.
   </para>

   <table id="datatype-binary-sqlesc">
    <title><type>bytea</> Literal Escaped Octets</title>
    <tgroup cols="5">
     <thead>
      <row>
       <entry>Decimal Octet Value</entry>
       <entry>Description</entry>
       <entry>Escaped Input Representation</entry>
       <entry>Example</entry>
       <entry>Output Representation</entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry>0</entry>
       <entry>zero octet</entry>
       <entry><literal>'\\000'</literal></entry>
       <entry><literal>SELECT '\\000'::bytea;</literal></entry>
       <entry><literal>\000</literal></entry>
      </row>

      <row>
       <entry>39</entry>
       <entry>single quote</entry>
       <entry><literal>'\''</literal> or <literal>'\\047'</literal></entry>
       <entry><literal>SELECT '\''::bytea;</literal></entry>
       <entry><literal>'</literal></entry>
      </row>

      <row>
       <entry>92</entry>
       <entry>backslash</entry>
       <entry><literal>'\\\\'</literal> or <literal>'\\134'</literal></entry>
       <entry><literal>SELECT '\\\\'::bytea;</literal></entry>
       <entry><literal>\\</literal></entry>
      </row>

      <row>
       <entry>0 to 31 and 127 to 255</entry>
       <entry><quote>non-printable</quote> octets</entry>
       <entry><literal>'\\<replaceable>xxx'</></literal> (octal value)</entry>
       <entry><literal>SELECT '\\001'::bytea;</literal></entry>
       <entry><literal>\001</literal></entry>
      </row>

     </tbody>
    </tgroup>
   </table>

   <para>
    The requirement to escape <quote>non-printable</quote> octets actually
    varies depending on locale settings. In some instances you can get away
    with leaving them unescaped. Note that the result in each of the examples
    in <xref linkend="datatype-binary-sqlesc"> was exactly one octet in
    length, even though the output representation of the zero octet and
    backslash are more than one character.
   </para>

   <para>
    The reason that you have to write so many backslashes, as shown in
    <xref linkend="datatype-binary-sqlesc">, is that an input string
    written as a string literal must pass through two parse phases in
    the <productname>PostgreSQL</productname> server.  The first
    backslash of each pair is interpreted as an escape character by
    the string-literal parser and is therefore consumed, leaving the
    second backslash of the pair.  The remaining backslash is then
    recognized by the <type>bytea</type> input function as starting
    either a three digit octal value or escaping another backslash.
    For example, a string literal passed to the server as
    <literal>'\\001'</literal> becomes <literal>\001</literal> after
    passing through the string-literal parser. The
    <literal>\001</literal> is then sent to the <type>bytea</type>
    input function, where it is converted to a single octet with a
    decimal value of 1.  Note that the apostrophe character is not
    treated specially by <type>bytea</type>, so it follows the normal
    rules for string literals.  (See also <xref
    linkend="sql-syntax-strings">.)
   </para>

   <para>
    <type>Bytea</type> octets are also escaped in the output. In general, each
    <quote>non-printable</quote> octet is converted into
    its equivalent three-digit octal value and preceded by one backslash.
    Most <quote>printable</quote> octets are represented by their standard
    representation in the client character set. The octet with decimal
    value 92 (backslash) has a special alternative output representation.
    Details are in <xref linkend="datatype-binary-resesc">.
   </para>

   <table id="datatype-binary-resesc">
    <title><type>bytea</> Output Escaped Octets</title>
    <tgroup cols="5">
     <thead>
      <row>
       <entry>Decimal Octet Value</entry>
       <entry>Description</entry>
       <entry>Escaped Output Representation</entry>
       <entry>Example</entry>
       <entry>Output Result</entry>
      </row>
     </thead>

     <tbody>

      <row>
       <entry>92</entry>
       <entry>backslash</entry>
       <entry><literal>\\</literal></entry>
       <entry><literal>SELECT '\\134'::bytea;</literal></entry>
       <entry><literal>\\</literal></entry>
      </row>

      <row>
       <entry>0 to 31 and 127 to 255</entry>
       <entry><quote>non-printable</quote> octets</entry>
       <entry><literal>\<replaceable>xxx</></literal> (octal value)</entry>
       <entry><literal>SELECT '\\001'::bytea;</literal></entry>
       <entry><literal>\001</literal></entry>
      </row>

      <row>
       <entry>32 to 126</entry>
       <entry><quote>printable</quote> octets</entry>
       <entry>client character set representation</entry>
       <entry><literal>SELECT '\\176'::bytea;</literal></entry>
       <entry><literal>~</literal></entry>
      </row>

     </tbody>
    </tgroup>
   </table>

   <para>
    Depending on the front end to <productname>PostgreSQL</> you use,
    you may have additional work to do in terms of escaping and
    unescaping <type>bytea</type> strings. For example, you may also
    have to escape line feeds and carriage returns if your interface
    automatically translates these.
   </para>

   <para>
        The <acronym>SQL</acronym> standard defines a different binary
        string type, called <type>BLOB</type> or <type>BINARY LARGE
         OBJECT</type>.  The input format is different compared to
        <type>bytea</type>, but the provided functions and operators are
        mostly the same.
   </para>
 </sect1>


  <sect1 id="datatype-datetime">
   <title>Date/Time Types</title>

   <indexterm zone="datatype-datetime">
    <primary>date</primary>
   </indexterm>
   <indexterm zone="datatype-datetime">
    <primary>time</primary>
   </indexterm>
   <indexterm zone="datatype-datetime">
    <primary>time without time zone</primary>
   </indexterm>
   <indexterm zone="datatype-datetime">
    <primary>time with time zone</primary>
   </indexterm>
   <indexterm zone="datatype-datetime">
    <primary>timestamp</primary>
   </indexterm>
   <indexterm zone="datatype-datetime">
    <primary>timestamp with time zone</primary>
   </indexterm>
   <indexterm zone="datatype-datetime">
    <primary>timestamp without time zone</primary>
   </indexterm>
   <indexterm zone="datatype-datetime">
    <primary>interval</primary>
   </indexterm>
   <indexterm zone="datatype-datetime">
    <primary>time span</primary>
   </indexterm>

   <para>
    <productname>PostgreSQL</productname> supports the full set of
    <acronym>SQL</acronym> date and time types, shown in <xref
    linkend="datatype-datetime-table">.
   </para>

    <table id="datatype-datetime-table">
     <title>Date/Time Types</title>
     <tgroup cols="6">
      <thead>
       <row>
        <entry>Name</entry>
        <entry>Storage Size</entry>
        <entry>Description</entry>
        <entry>Low Value</entry>
        <entry>High Value</entry>
        <entry>Resolution</entry>
       </row>
      </thead>
      <tbody>
       <row>
        <entry><type>timestamp [ (<replaceable>p</replaceable>) ] [ without time zone ]</type></entry>
        <entry>8 bytes</entry>
        <entry>both date and time</entry>
        <entry>4713 BC</entry>
        <entry>5874897 AD</entry>
        <entry>1 microsecond / 14 digits</entry>
       </row>
       <row>
        <entry><type>timestamp [ (<replaceable>p</replaceable>) ] with time zone</type></entry>
        <entry>8 bytes</entry>
        <entry>both date and time, with time zone</entry>
        <entry>4713 BC</entry>
        <entry>5874897 AD</entry>
        <entry>1 microsecond / 14 digits</entry>
       </row>
       <row>
        <entry><type>interval [ (<replaceable>p</replaceable>) ]</type></entry>
        <entry>12 bytes</entry>
        <entry>time intervals</entry>
        <entry>-178000000 years</entry>
        <entry>178000000 years</entry>
        <entry>1 microsecond</entry>
       </row>
       <row>
        <entry><type>date</type></entry>
        <entry>4 bytes</entry>
        <entry>dates only</entry>
        <entry>4713 BC</entry>
        <entry>32767 AD</entry>
        <entry>1 day</entry>
       </row>
       <row>
        <entry><type>time [ (<replaceable>p</replaceable>) ] [ without time zone ]</type></entry>
        <entry>8 bytes</entry>
        <entry>times of day only</entry>
        <entry>00:00:00.00</entry>
        <entry>23:59:59.99</entry>
        <entry>1 microsecond</entry>
       </row>
       <row>
        <entry><type>time [ (<replaceable>p</replaceable>) ] with time zone</type></entry>
        <entry>12 bytes</entry>
        <entry>times of day only, with time zone</entry>
        <entry>00:00:00.00+12</entry>
        <entry>23:59:59.99-12</entry>
        <entry>1 microsecond</entry>
       </row>
      </tbody>
     </tgroup>
    </table>

   <note>
    <para>
     Prior to <productname>PostgreSQL</productname> 7.3, writing just
     <type>timestamp</type> was equivalent to <type>timestamp with
     time zone</type>.  This was changed for SQL compliance.
    </para>
   </note>

   <para>
    <type>time</type>, <type>timestamp</type>, and
    <type>interval</type> accept an optional precision value
    <replaceable>p</replaceable> which specifies the number of
    fractional digits retained in the seconds field. By default, there
    is no explicit bound on precision.  The allowed range of
    <replaceable>p</replaceable> is from 0 to 6 for the
    <type>timestamp</type> and <type>interval</type> types.
   </para>

   <note>
   <para>
    When <type>timestamp</> values are stored as double precision floating-point
    numbers (currently the default), the effective limit of precision
    may be less than 6. <type>timestamp</type> values are stored as seconds
    before or after midnight 2000-01-01.  Microsecond precision is achieved for
    dates within a few years of 2000-01-01, but the precision degrades for
    dates further away.  When <type>timestamp</type> values are stored as
    eight-byte integers (a compile-time
    option), microsecond precision is available over the full range of
    values. However eight-byte integer timestamps have a more limited range of
    dates than shown above: from 4713 BC up to 294276 AD.
   </para>
   </note>

   <para>
    For the <type>time</type> types, the allowed range of
    <replaceable>p</replaceable> is from 0 to 6 when eight-byte integer
    storage is used, or from 0 to 10 when floating-point storage is used.
   </para>

   <para>
    The type <type>time with time zone</type> is defined by the SQL
    standard, but the definition exhibits properties which lead to
    questionable usefulness. In most cases, a combination of
    <type>date</type>, <type>time</type>, <type>timestamp without time
    zone</type>, and <type>timestamp with time zone</type> should
    provide a complete range of date/time functionality required by
    any application.
   </para>

   <para>
    The types <type>abstime</type>
    and <type>reltime</type> are lower precision types which are used internally.
    You are discouraged from using these types in new
    applications and are encouraged to move any old
    ones over when appropriate. Any or all of these internal types
    might disappear in a future release.
   </para>

   <sect2 id="datatype-datetime-input">
    <title>Date/Time Input</title>

    <para>
     Date and time input is accepted in almost any reasonable format, including
     ISO 8601, <acronym>SQL</acronym>-compatible, 
     traditional <productname>POSTGRES</productname>, and others.
     For some formats, ordering of month, day, and year in date input is
     ambiguous and there is support for specifying the expected
     ordering of these fields.  Set the <varname>datestyle</> parameter
     to <literal>MDY</> to select month-day-year interpretation,
     <literal>DMY</> to select day-month-year interpretation, or
     <literal>YMD</> to select year-month-day interpretation.
    </para>

    <para>
     <productname>PostgreSQL</productname> is more flexible in
     handling date/time input than the
     <acronym>SQL</acronym> standard requires.
     See <xref linkend="datetime-appendix">
     for the exact parsing rules of date/time input and for the
     recognized text fields including months, days of the week, and
     time zones. 
    </para>

    <para>
     Remember that any date or time literal input needs to be enclosed
     in single quotes, like text strings.  Refer to 
     <xref linkend="sql-syntax-constants-generic"> for more
     information.
     <acronym>SQL</acronym> requires the following syntax
<synopsis>
<replaceable>type</replaceable> [ (<replaceable>p</replaceable>) ] '<replaceable>value</replaceable>'
</synopsis>
     where <replaceable>p</replaceable> in the optional precision
     specification is an integer corresponding to the number of
     fractional digits in the seconds field. Precision can be
     specified for <type>time</type>, <type>timestamp</type>, and
     <type>interval</type> types.  The allowed values are mentioned
     above.  If no precision is specified in a constant specification,
     it defaults to the precision of the literal value.
    </para>

    <sect3>
    <title>Dates</title>

    <indexterm>
     <primary>date</primary>
    </indexterm>
 
    <para>
     <xref linkend="datatype-datetime-date-table"> shows some possible
     inputs for the <type>date</type> type.
    </para>

     <table id="datatype-datetime-date-table">
      <title>Date Input</title>
      <tgroup cols="2">
       <thead>
        <row>
         <entry>Example</entry>
         <entry>Description</entry>
        </row>
       </thead>
       <tbody>
        <row>
         <entry>January 8, 1999</entry>
         <entry>unambiguous in any <varname>datestyle</varname> input mode</entry>
        </row>
        <row>
         <entry>1999-01-08</entry>
         <entry>ISO 8601; January 8 in any mode
         (recommended format)</entry>
        </row>
        <row>
         <entry>1/8/1999</entry>
         <entry>January 8 in <literal>MDY</> mode;
          August 1 in <literal>DMY</> mode</entry>
        </row>
        <row>
         <entry>1/18/1999</entry>
         <entry>January 18 in <literal>MDY</> mode;
          rejected in other modes</entry>
        </row>
        <row>
         <entry>01/02/03</entry>
         <entry>January 2, 2003 in <literal>MDY</> mode;
          February 1, 2003 in <literal>DMY</> mode;
          February 3, 2001 in <literal>YMD</> mode
         </entry>
        </row>
        <row>
         <entry>1999-Jan-08</entry>
         <entry>January 8 in any mode</entry>
        </row>
        <row>
         <entry>Jan-08-1999</entry>
         <entry>January 8 in any mode</entry>
        </row>
        <row>
         <entry>08-Jan-1999</entry>
         <entry>January 8 in any mode</entry>
        </row>
        <row>
         <entry>99-Jan-08</entry>
         <entry>January 8 in <literal>YMD</> mode, else error</entry>
        </row>
        <row>
         <entry>08-Jan-99</entry>
         <entry>January 8, except error in <literal>YMD</> mode</entry>
        </row>
        <row>
         <entry>Jan-08-99</entry>
         <entry>January 8, except error in <literal>YMD</> mode</entry>
        </row>
        <row>
         <entry>19990108</entry>
         <entry>ISO 8601; January 8, 1999 in any mode</entry>
        </row>
        <row>
         <entry>990108</entry>
         <entry>ISO 8601; January 8, 1999 in any mode</entry>
        </row>
        <row>
         <entry>1999.008</entry>
         <entry>year and day of year</entry>
        </row>
        <row>
         <entry>J2451187</entry>
         <entry>Julian day</entry>
        </row>
        <row>
         <entry>January 8, 99 BC</entry>
         <entry>year 99 before the Common Era</entry>
        </row>
       </tbody>
      </tgroup>
     </table>
    </sect3>

    <sect3>
     <title>Times</title>

     <indexterm>
      <primary>time</primary>
     </indexterm>
     <indexterm>
      <primary>time without time zone</primary>
     </indexterm>
     <indexterm>
      <primary>time with time zone</primary>
     </indexterm>

     <para>
      The time-of-day types are <type>time [
      (<replaceable>p</replaceable>) ] without time zone</type> and
      <type>time [ (<replaceable>p</replaceable>) ] with time
      zone</type>.  Writing just <type>time</type> is equivalent to
      <type>time without time zone</type>.
     </para>

     <para>
      Valid input for these types consists of a time of day followed
      by an optional time zone. (See <xref
      linkend="datatype-datetime-time-table"> 
      and <xref linkend="datatype-timezone-table">.)  If a time zone is
      specified in the input for <type>time without time zone</type>,
      it is silently ignored.
     </para>

      <table id="datatype-datetime-time-table">
       <title>Time Input</title>
       <tgroup cols="2">
        <thead>
         <row>
          <entry>Example</entry>
          <entry>Description</entry>
         </row>
        </thead>
        <tbody>
         <row>
          <entry><literal>04:05:06.789</literal></entry>
          <entry>ISO 8601</entry>
         </row>
         <row>
          <entry><literal>04:05:06</literal></entry>
          <entry>ISO 8601</entry>
         </row>
         <row>
          <entry><literal>04:05</literal></entry>
          <entry>ISO 8601</entry>
         </row>
         <row>
          <entry><literal>040506</literal></entry>
          <entry>ISO 8601</entry>
         </row>
         <row>
          <entry><literal>04:05 AM</literal></entry>
          <entry>same as 04:05; AM does not affect value</entry>
         </row>
         <row>
          <entry><literal>04:05 PM</literal></entry>
          <entry>same as 16:05; input hour must be <= 12</entry>
         </row>
         <row>
          <entry><literal>04:05:06.789-8</literal></entry>
          <entry>ISO 8601</entry>
         </row>
         <row>
          <entry><literal>04:05:06-08:00</literal></entry>
          <entry>ISO 8601</entry>
         </row>
         <row>
          <entry><literal>04:05-08:00</literal></entry>
          <entry>ISO 8601</entry>
         </row>
         <row>
          <entry><literal>040506-08</literal></entry>
          <entry>ISO 8601</entry>
         </row>
         <row>
          <entry><literal>04:05:06 PST</literal></entry>
          <entry>time zone specified by name</entry>
         </row>
        </tbody>
       </tgroup>
      </table>

      <table tocentry="1" id="datatype-timezone-table">
       <title>Time Zone Input</title>
       <tgroup cols="2">
        <thead>
         <row>
          <entry>Example</entry>
          <entry>Description</entry>
         </row>
        </thead>
        <tbody>
         <row>
          <entry><literal>PST</literal></entry>
          <entry>Pacific Standard Time</entry>
         </row>
         <row>
          <entry><literal>-8:00</literal></entry>
          <entry>ISO-8601 offset for PST</entry>
         </row>
         <row>
          <entry><literal>-800</literal></entry>
          <entry>ISO-8601 offset for PST</entry>
         </row>
         <row>
          <entry><literal>-8</literal></entry>
          <entry>ISO-8601 offset for PST</entry>
         </row>
         <row>
          <entry><literal>zulu</literal></entry>
          <entry>Military abbreviation for UTC</entry>
         </row>
         <row>
          <entry><literal>z</literal></entry>
          <entry>Short form of <literal>zulu</literal></entry>
         </row>
        </tbody>
       </tgroup>
      </table>
    </sect3>

    <sect3>
    <title>Time Stamps</title>

    <indexterm>
     <primary>timestamp</primary>
    </indexterm>

    <indexterm>
     <primary>timestamp with time zone</primary>
    </indexterm>

    <indexterm>
     <primary>timestamp without time zone</primary>
    </indexterm>

     <para>
      Valid input for the time stamp types consists of a concatenation
      of a date and a time, followed by an optional
      <literal>AD</literal> or <literal>BC</literal>, followed by an
      optional time zone. Thus

<programlisting>
1999-01-08 04:05:06
</programlisting>
      and
<programlisting>
1999-01-08 04:05:06 -8:00
</programlisting>

      are valid values, which follow the <acronym>ISO</acronym> 8601
      standard.  In addition, the wide-spread format

<programlisting>
January 8 04:05:06 1999 PST
</programlisting>
      is supported.
     </para>

     <para>
      For <type>timestamp [without time zone]</type>, any explicit time
      zone specified in the input is silently ignored. That is, the
      resulting date/time value is derived from the explicit date/time
      fields in the input value, and is not adjusted for time zone.
     </para>

     <para>
      For <type>timestamp with time zone</type>, the internally stored
      value is always in UTC (Universal
      Coordinated Time, traditionally known as Greenwich Mean Time,
      <acronym>GMT</>).  An input value that has an explicit
      time zone specified is converted to UTC using the appropriate offset
      for that time zone.  If no time zone is stated in the input string,
      then it is assumed to be in the time zone indicated by the system's
      <varname>timezone</> parameter, and is converted to UTC using the
      offset for the <varname>timezone</> zone.
     </para>

     <para>
      When a <type>timestamp with time
      zone</type> value is output, it is always converted from UTC to the
      current <varname>timezone</> zone, and displayed as local time in that
      zone.  To see the time in another time zone, either change
      <varname>timezone</> or use the <literal>AT TIME ZONE</> construct
      (see <xref linkend="functions-datetime-zoneconvert">).
     </para>

     <para>
      Conversions between <type>timestamp without time zone</type> and
      <type>timestamp with time zone</type> normally assume that the
      <type>timestamp without time zone</type> value should be taken or given
      as <varname>timezone</> local time.  A different zone reference can
      be specified for the conversion using <literal>AT TIME ZONE</>.
     </para>
    </sect3>

    <sect3>
     <title>Intervals</title>

     <indexterm>
      <primary>interval</primary>
     </indexterm>

      <para>
       <type>interval</type> values can be written with the following syntax:

<programlisting>
<optional>@</> <replaceable>quantity</> <replaceable>unit</> <optional><replaceable>quantity</> <replaceable>unit</>...</> <optional><replaceable>direction</></optional>
</programlisting>

      Where: <replaceable>quantity</> is a number (possibly signed);
      <replaceable>unit</> is <literal>second</literal>,
      <literal>minute</literal>, <literal>hour</literal>, <literal>day</literal>,
      <literal>week</literal>, <literal>month</literal>, <literal>year</literal>,
      <literal>decade</literal>, <literal>century</literal>, <literal>millennium</literal>,
      or abbreviations or plurals of these units;
      <replaceable>direction</> can be <literal>ago</literal> or
      empty.  The at sign (<literal>@</>) is optional noise.  The amounts
      of different units are implicitly added up with appropriate
      sign accounting.
     </para>

     <para>
      Quantities of days, hours, minutes, and seconds can be specified without
      explicit unit markings.  For example, <literal>'1 12:59:10'</> is read
      the same as <literal>'1 day 12 hours 59 min 10 sec'</>.
     </para>

     <para>
      The optional precision
      <replaceable>p</replaceable> should be between 0 and 6, and
      defaults to the precision of the input literal.
     </para>
    </sect3>

    <sect3>
     <title>Special Values</title>

     <indexterm>
      <primary>time</primary>
      <secondary>constants</secondary>
     </indexterm>

     <indexterm>
      <primary>date</primary>
      <secondary>constants</secondary>
     </indexterm>

     <para>
      The following <acronym>SQL</acronym>-compatible functions can be
      used as date or time values for the corresponding data type: 
      <literal>CURRENT_DATE</literal>, <literal>CURRENT_TIME</literal>, 
      <literal>CURRENT_TIMESTAMP</literal>, <literal>LOCALTIME</literal>, 
      <literal>LOCALTIMESTAMP</literal>.  The latter four accept an 
      optional precision specification.  (See also <xref 
      linkend="functions-datetime-current">.)
     </para>

     <para>
      <productname>PostgreSQL</productname> also supports several
      special date/time input values for convenience, as shown in <xref
      linkend="datatype-datetime-special-table">.  The values
      <literal>infinity</literal> and <literal>-infinity</literal>
      are specially represented inside the system and will be displayed
      the same way; but the others are simply notational shorthands
      that will be converted to ordinary date/time values when read.
      All of these values are treated as normal constants and need to be
      written in single quotes.
     </para>

      <table id="datatype-datetime-special-table">
       <title>Special Date/Time Inputs</title>
       <tgroup cols="2">
        <thead>
         <row>
          <entry>Input String</entry>
          <entry>Valid Types</entry>
          <entry>Description</entry>
         </row>
        </thead>
        <tbody>
         <row>
          <entry><literal>epoch</literal></entry>
          <entry><type>date</type>, <type>timestamp</type></entry>
          <entry>1970-01-01 00:00:00+00 (Unix system time zero)</entry>
         </row>
         <row>
          <entry><literal>infinity</literal></entry>
          <entry><type>timestamp</type></entry>
          <entry>later than all other time stamps</entry>
         </row>
         <row>
          <entry><literal>-infinity</literal></entry>
          <entry><type>timestamp</type></entry>
          <entry>earlier than all other time stamps</entry>
         </row>
         <row>
          <entry><literal>now</literal></entry>
          <entry><type>date</type>, <type>time</type>, <type>timestamp</type></entry>
          <entry>current transaction's start time</entry>
         </row>
         <row>
          <entry><literal>today</literal></entry>
          <entry><type>date</type>, <type>timestamp</type></entry>
          <entry>midnight today</entry>
         </row>
         <row>
          <entry><literal>tomorrow</literal></entry>
          <entry><type>date</type>, <type>timestamp</type></entry>
          <entry>midnight tomorrow</entry>
         </row>
         <row>
          <entry><literal>yesterday</literal></entry>
          <entry><type>date</type>, <type>timestamp</type></entry>
          <entry>midnight yesterday</entry>
         </row>
         <row>
          <entry><literal>allballs</literal></entry>
          <entry><type>time</type></entry>
          <entry>00:00:00.00 UTC</entry>
         </row>
        </tbody>
       </tgroup>
      </table>

    </sect3>
   </sect2>

   <sect2 id="datatype-datetime-output">
    <title>Date/Time Output</title>

    <indexterm>
     <primary>date</primary>
     <secondary>output format</secondary>
     <seealso>formatting</seealso>
    </indexterm>

    <indexterm>
     <primary>time</primary>
     <secondary>output format</secondary>
     <seealso>formatting</seealso>
    </indexterm>

    <para>
     The output format of the date/time types can be set to one of the four
     styles ISO 8601,
     <acronym>SQL</acronym> (Ingres), traditional POSTGRES, and
     German, using the command <literal>SET datestyle</literal>.  The default
     is the <acronym>ISO</acronym> format.  (The
     <acronym>SQL</acronym> standard requires the use of the ISO 8601
     format.  The name of the <quote>SQL</quote> output format is a
     historical accident.)  <xref
     linkend="datatype-datetime-output-table"> shows examples of each
     output style.  The output of the <type>date</type> and
     <type>time</type> types is of course only the date or time part
     in accordance with the given examples.
    </para>

     <table id="datatype-datetime-output-table">
      <title>Date/Time Output Styles</title>
      <tgroup cols="3">
       <thead>
        <row>
         <entry>Style Specification</entry>
         <entry>Description</entry>
         <entry>Example</entry>
        </row>
       </thead>
       <tbody>
        <row>
         <entry>ISO</entry>
         <entry>ISO 8601/SQL standard</entry>
         <entry>1997-12-17 07:37:16-08</entry>
        </row>
        <row>
         <entry>SQL</entry>
         <entry>traditional style</entry>
         <entry>12/17/1997 07:37:16.00 PST</entry>
        </row>
        <row>
         <entry>POSTGRES</entry>
         <entry>original style</entry>
         <entry>Wed Dec 17 07:37:16 1997 PST</entry>
        </row>
        <row>
         <entry>German</entry>
         <entry>regional style</entry>
         <entry>17.12.1997 07:37:16.00 PST</entry>
        </row>
       </tbody>
      </tgroup>
     </table>

    <para>
     In the <acronym>SQL</acronym> and POSTGRES styles, day appears before
     month if DMY field ordering has been specified, otherwise month appears
     before day.
     (See <xref linkend="datatype-datetime-input">
     for how this setting also affects interpretation of input values.)
     <xref linkend="datatype-datetime-output2-table"> shows an
     example.
    </para>

     <table id="datatype-datetime-output2-table">
      <title>Date Order Conventions</title>
      <tgroup cols="3">
       <thead>
        <row>
         <entry><varname>datestyle</varname> Setting</entry>
         <entry>Input Ordering</entry>
         <entry>Example Output</entry>
        </row>
       </thead>
       <tbody>
        <row>
         <entry><literal>SQL, DMY</></entry>
         <entry><replaceable>day</replaceable>/<replaceable>month</replaceable>/<replaceable>year</replaceable></entry>
         <entry>17/12/1997 15:37:16.00 CET</entry>
        </row>
        <row>
         <entry><literal>SQL, MDY</></entry>
         <entry><replaceable>month</replaceable>/<replaceable>day</replaceable>/<replaceable>year</replaceable></entry>
         <entry>12/17/1997 07:37:16.00 PST</entry>
        </row>
        <row>
         <entry><literal>Postgres, DMY</></entry>
         <entry><replaceable>day</replaceable>/<replaceable>month</replaceable>/<replaceable>year</replaceable></entry>
         <entry>Wed 17 Dec 07:37:16 1997 PST</entry>
        </row>
       </tbody>
      </tgroup>
     </table>

    <para>
     <type>interval</type> output looks like the input format, except
     that units like <literal>century</literal> or
     <literal>wek</literal> are converted to years and days and that
     <literal>ago</literal> is converted to an appropriate sign.  In
     ISO mode the output looks like

<programlisting>
<optional> <replaceable>quantity</> <replaceable>unit</> <optional> ... </> </> <optional> <replaceable>days</> </> <optional> <replaceable>hours</>:<replaceable>minutes</>:<replaceable>sekunden</> </optional>
</programlisting>
    </para>

    <para>
     The date/time styles can be selected by the user using the
     <command>SET datestyle</command> command, the
     <varname>datestyle</varname> parameter in the
     <filename>postgresql.conf</filename> configuration file, or the
     <envar>PGDATESTYLE</envar> environment variable on the server or
     client.  The formatting function <function>to_char</function>
     (see <xref linkend="functions-formatting">) is also available as
     a more flexible way to format the date/time output.
    </para>
   </sect2>

   <sect2 id="datatype-timezones">
    <title>Time Zones</title>

    <indexterm zone="datatype-timezones">
     <primary>time zone</primary>
    </indexterm>

   <para>
    Time zones, and time-zone conventions, are influenced by
    political decisions, not just earth geometry. Time zones around the
    world became somewhat standardized during the 1900's,
    but continue to be prone to arbitrary changes.
    <productname>PostgreSQL</productname> uses your operating
    system's underlying features to provide output time-zone
    support, and these systems usually contain information for only
    the time period 1902 through 2038 (corresponding to the full
    range of conventional Unix system time).
    <type>timestamp with time zone</type> and <type>time with time
     zone</type> will use time zone
    information only within that year range, and assume that times
    outside that range are in <acronym>UTC</acronym>.
    But since time zone support is derived from the underlying operating
    system time-zone capabilities, it can handle daylight-saving time
    and other special behavior.
   </para>

    <para>
     <productname>PostgreSQL</productname> endeavors to be compatible with
     the <acronym>SQL</acronym> standard definitions for typical usage.
     However, the <acronym>SQL</acronym> standard has an odd mix of date and
     time types and capabilities. Two obvious problems are:

     <itemizedlist>
      <listitem>
       <para>
        Although the <type>date</type> type 
        does not have an associated time zone, the
        <type>time</type> type can.
        Time zones in the real world can have no meaning unless 
        associated with a date as well as a time
        since the offset may vary through the year with daylight-saving
        time boundaries.
       </para>
      </listitem>

      <listitem>
       <para>
        The default time zone is specified as a constant numeric offset 
        from <acronym>UTC</>. It is not possible to adapt to daylight-saving
        time when doing date/time arithmetic across
        <acronym>DST</acronym> boundaries.
       </para>
      </listitem>

     </itemizedlist>
    </para>

    <para>
     To address these difficulties, we recommend using date/time types
     that contain both date and time when using time zones. We
     recommend <emphasis>not</emphasis> using the type <type>time with
     time zone</type> (though it is supported by
     <productname>PostgreSQL</productname> for legacy applications and
     for compatibility with other <acronym>SQL</acronym>
     implementations).  <productname>PostgreSQL</productname> assumes
     your local time zone for any type containing only date or time.
    </para>

    <para>
     All dates and times are stored internally in
     <acronym>UTC</acronym>.  Times are converted to local time
     on the database server before being sent to the client,
     hence by default are in the server time zone.
    </para>

    <para>
     There are several ways to select the time zone used by the server:

     <itemizedlist>
      <listitem>
       <para>
        The <envar>TZ</envar> environment variable on the server host
        is used by the server as the default time zone, if no other is
        specified.
       </para>
      </listitem>

      <listitem>
       <para>
        The <varname>timezone</varname> configuration parameter can be
        set in the file <filename>postgresql.conf</>.
       </para>
      </listitem>

      <listitem>
       <para>
        The <envar>PGTZ</envar> environment variable, if set at the
        client, is used by <application>libpq</application>
        applications to send a <command>SET TIME ZONE</command>
        command to the server upon connection.
       </para>
      </listitem>

      <listitem>
       <para>
        The <acronym>SQL</acronym> command <command>SET TIME ZONE</command>
        sets the time zone for the session.
       </para>
      </listitem>
     </itemizedlist>
    </para>

     <note>
      <para>
       If an invalid time zone is specified, the time zone becomes
       <acronym>UTC</acronym> (on most systems anyway).
      </para>
     </note>

   <para>
    Refer to <xref linkend="datetime-appendix"> for a list of
    available time zones.
   </para>

   </sect2>

   <sect2 id="datatype-datetime-internals">
    <title>Internals</title>

    <para>
     <productname>PostgreSQL</productname> uses Julian dates
     for all date/time calculations. They have the nice property of correctly
     predicting/calculating any date more recent than 4713 BC
     to far into the future, using the assumption that the length of the
     year is 365.2425 days.
    </para>

    <para>
     Date conventions before the 19th century make for interesting reading,
     but are not consistent enough to warrant coding into a date/time handler.
    </para>
   </sect2>

  </sect1>

  <sect1 id="datatype-boolean">
   <title>Boolean Type</title>

   <indexterm zone="datatype-boolean">
    <primary>Boolean</primary>
    <secondary>data type</secondary>
   </indexterm>

   <indexterm zone="datatype-boolean">
    <primary>true</primary>
   </indexterm>

   <indexterm zone="datatype-boolean">
    <primary>false</primary>
   </indexterm>

   <para>
    <productname>PostgreSQL</productname> provides the
    standard <acronym>SQL</acronym> type <type>boolean</type>.
    <type>boolean</type> can have one of only two states:
    <quote>true</quote> or <quote>false</quote>.  A third state,
    <quote>unknown</quote>, is represented by the
    <acronym>SQL</acronym> null value.
   </para>

   <para>
    Valid literal values for the <quote>true</quote> state are:
    <simplelist>
     <member><literal>TRUE</literal></member>
     <member><literal>'t'</literal></member>
     <member><literal>'true'</literal></member>
     <member><literal>'y'</literal></member>
     <member><literal>'yes'</literal></member>
     <member><literal>'1'</literal></member>
    </simplelist>
    For the <quote>false</quote> state, the following values can be
    used:
    <simplelist>
     <member><literal>FALSE</literal></member>
     <member><literal>'f'</literal></member>
     <member><literal>'false'</literal></member>
     <member><literal>'n'</literal></member>
     <member><literal>'no'</literal></member>
     <member><literal>'0'</literal></member>
    </simplelist>
    Using the key words <literal>TRUE</literal> and
    <literal>FALSE</literal> is preferred (and
    <acronym>SQL</acronym>-compliant).
   </para>

   <example id="datatype-boolean-example">
    <title>Using the <type>boolean</type> type</title>

<programlisting>
CREATE TABLE test1 (a boolean, b text);
INSERT INTO test1 VALUES (TRUE, 'sic est');
INSERT INTO test1 VALUES (FALSE, 'non est');
SELECT * FROM test1;
 a |    b
---+---------
 t | sic est
 f | non est

SELECT * FROM test1 WHERE a;
 a |    b
---+---------
 t | sic est
</programlisting>
   </example>

   <para>
    <xref linkend="datatype-boolean-example"> shows that
    <type>boolean</type> values are output using the letters
    <literal>t</literal> and <literal>f</literal>.
   </para>

   <tip>
    <para>
     Values of the <type>boolean</type> type cannot be cast directly
     to other types (e.g., <literal>CAST
     (<replaceable>boolval</replaceable> AS integer)</literal> does
     not work).  This can be accomplished using the
     <literal>CASE</literal> expression: <literal>CASE WHEN
     <replaceable>boolval</replaceable> THEN 'value if true' ELSE
     'value if false' END</literal>.  See also <xref
     linkend="functions-conditional">.
    </para>
   </tip>

   <para>
    <type>boolean</type> uses 1 byte of storage.
   </para>
  </sect1>

  <sect1 id="datatype-geometric">
   <title>Geometric Types</title>

   <para>
    Geometric data types represent two-dimensional spatial
    objects. <xref linkend="datatype-geo-table"> shows the geometric
    types available in <productname>PostgreSQL</productname>.  The
    most fundamental type, the point, forms the basis for all of the
    other types.
   </para>

    <table id="datatype-geo-table">
     <title>Geometric Types</title>
     <tgroup cols="4">
      <thead>
       <row>
        <entry>Name</entry>
        <entry>Storage Size</entry>
        <entry>Representation</entry>
        <entry>Description</entry>
       </row>
      </thead>
      <tbody>
       <row>
        <entry><type>point</type></entry>
        <entry>16 bytes</entry>
        <entry>Point on the plane</entry>
        <entry>(x,y)</entry>
       </row>
       <row>
        <entry><type>line</type></entry>
        <entry>32 bytes</entry>
        <entry>Infinite line (not fully implemented)</entry>
        <entry>((x1,y1),(x2,y2))</entry>
       </row>
       <row>
        <entry><type>lseg</type></entry>
        <entry>32 bytes</entry>
        <entry>Finite line segment</entry>
        <entry>((x1,y1),(x2,y2))</entry>
       </row>
       <row>
        <entry><type>box</type></entry>
        <entry>32 bytes</entry>
        <entry>Rectangular box</entry>
        <entry>((x1,y1),(x2,y2))</entry>
       </row>
       <row>
        <entry><type>path</type></entry>
        <entry>16+16n bytes</entry>
        <entry>Closed path (similar to polygon)</entry>
        <entry>((x1,y1),...)</entry>
       </row>
       <row>
        <entry><type>path</type></entry>
        <entry>16+16n bytes</entry>
        <entry>Open path</entry>
        <entry>[(x1,y1),...]</entry>
       </row>
       <row>
        <entry><type>polygon</type></entry>
        <entry>40+16n bytes</entry>
        <entry>Polygon (similar to closed path)</entry>
        <entry>((x1,y1),...)</entry>
       </row>
       <row>
        <entry><type>circle</type></entry>
        <entry>24 bytes</entry>
        <entry>Circle</entry>
        <entry><(x,y),r> (center and radius)</entry>
       </row>
      </tbody>
     </tgroup>
    </table>

   <para>
    A rich set of functions and operators is available to perform various geometric
    operations such as scaling, translation, rotation, and determining 
    intersections.  They are explained in <xref linkend="functions-geometry">.
   </para>

   <sect2>
    <title>Points</title>

    <indexterm>
     <primary>point</primary>
    </indexterm>

    <para>
     Points are the fundamental two-dimensional building block for geometric types.
     Values of type <type>point</type> are specified using the following syntax:

<synopsis>
( <replaceable>x</replaceable> , <replaceable>y</replaceable> )
  <replaceable>x</replaceable> , <replaceable>y</replaceable>
</synopsis>

     where <replaceable>x</> and <replaceable>y</> are the respective
     coordinates as floating-point numbers.
    </para>
   </sect2>

   <sect2>
    <title>Line Segments</title>

    <indexterm>
     <primary>lseg</primary>
    </indexterm>

    <indexterm>
     <primary>line segment</primary>
    </indexterm>

    <para>
     Line segments (<type>lseg</type>) are represented by pairs of points.
     Values of type <type>lseg</type> are specified using the following syntax:

<synopsis>
( ( <replaceable>x1</replaceable> , <replaceable>y1</replaceable> ) , ( <replaceable>x2</replaceable> , <replaceable>y2</replaceable> ) )
  ( <replaceable>x1</replaceable> , <replaceable>y1</replaceable> ) , ( <replaceable>x2</replaceable> , <replaceable>y2</replaceable> )  
    <replaceable>x1</replaceable> , <replaceable>y1</replaceable>   ,   <replaceable>x2</replaceable> , <replaceable>y2</replaceable>
</synopsis>

     where
     <literal>(<replaceable>x1</replaceable>,<replaceable>y1</replaceable>)</literal>
     and
     <literal>(<replaceable>x2</replaceable>,<replaceable>y2</replaceable>)</literal>
     are the end points of the line segment.
    </para>
   </sect2>

   <sect2>
    <title>Boxes</title>

    <indexterm>
     <primary>box (data type)</primary>
    </indexterm>

    <indexterm>
     <primary>rectangle</primary>
    </indexterm>

    <para>
     Boxes are represented by pairs of points that are opposite
     corners of the box.
     Values of type <type>box</type> is specified using the following syntax:

<synopsis>
( ( <replaceable>x1</replaceable> , <replaceable>y1</replaceable> ) , ( <replaceable>x2</replaceable> , <replaceable>y2</replaceable> ) )
  ( <replaceable>x1</replaceable> , <replaceable>y1</replaceable> ) , ( <replaceable>x2</replaceable> , <replaceable>y2</replaceable> )  
    <replaceable>x1</replaceable> , <replaceable>y1</replaceable>   ,   <replaceable>x2</replaceable> , <replaceable>y2</replaceable>
</synopsis>

     where
     <literal>(<replaceable>x1</replaceable>,<replaceable>y1</replaceable>)</literal>
     and
     <literal>(<replaceable>x2</replaceable>,<replaceable>y2</replaceable>)</literal>
     are the opposite corners of the box.
    </para>

    <para>
     Boxes are output using the first syntax.
     The corners are reordered on input to store
     the upper right corner, then the lower left corner.
     Other corners of the box can be entered, but the lower
     left and upper right corners are determined from the input and stored corners.
    </para>
   </sect2>

   <sect2>
    <title>Paths</title>

    <indexterm>
     <primary>path (data type)</primary>
    </indexterm>

    <para>
     Paths are represented by connected sets of points. Paths can be
     <firstterm>open</firstterm>, where
     the first and last points in the set are not connected, and <firstterm>closed</firstterm>,
     where the first and last point are connected. The functions
     <function>popen(<replaceable>p</>)</function>
     and
     <function>pclose(<replaceable>p</>)</function>
     are supplied to force a path to be open or closed, and the functions
     <function>isopen(<replaceable>p</>)</function>
     and
     <function>isclosed(<replaceable>p</>)</function>
     are supplied to test for either type in an expression.
    </para>

    <para>
     Values of type <type>path</type> are specified using the following syntax:

<synopsis>
( ( <replaceable>x1</replaceable> , <replaceable>y1</replaceable> ) , ... , ( <replaceable>xn</replaceable> , <replaceable>yn</replaceable> ) )
[ ( <replaceable>x1</replaceable> , <replaceable>y1</replaceable> ) , ... , ( <replaceable>xn</replaceable> , <replaceable>yn</replaceable> ) ]
  ( <replaceable>x1</replaceable> , <replaceable>y1</replaceable> ) , ... , ( <replaceable>xn</replaceable> , <replaceable>yn</replaceable> )  
  ( <replaceable>x1</replaceable> , <replaceable>y1</replaceable>   , ... ,   <replaceable>xn</replaceable> , <replaceable>yn</replaceable> )  
    <replaceable>x1</replaceable> , <replaceable>y1</replaceable>   , ... ,   <replaceable>xn</replaceable> , <replaceable>yn</replaceable>    
</synopsis>

     where the points are the end points of the line segments
     comprising the path.  Square brackets (<literal>[]</>) indicate
     an open path, while parentheses (<literal>()</>) indicate a
     closed path.
    </para>

    <para>
     Paths are output using the first syntax.
    </para>
   </sect2>

   <sect2>
    <title>Polygons</title>

    <indexterm>
     <primary>polygon</primary>
    </indexterm>

    <para>
     Polygons are represented by sets of points. Polygons should probably be
     considered equivalent to closed paths, but are stored differently 
     and have their own set of support routines.
    </para>

    <para>
     Values of type <type>polygon</type> are specified using the following syntax:

<synopsis>
( ( <replaceable>x1</replaceable> , <replaceable>y1</replaceable> ) , ... , ( <replaceable>xn</replaceable> , <replaceable>yn</replaceable> ) )
  ( <replaceable>x1</replaceable> , <replaceable>y1</replaceable> ) , ... , ( <replaceable>xn</replaceable> , <replaceable>yn</replaceable> )  
  ( <replaceable>x1</replaceable> , <replaceable>y1</replaceable>   , ... ,   <replaceable>xn</replaceable> , <replaceable>yn</replaceable> )  
    <replaceable>x1</replaceable> , <replaceable>y1</replaceable>   , ... ,   <replaceable>xn</replaceable> , <replaceable>yn</replaceable>    
</synopsis>

     where the points are the end points of the line segments
     comprising the boundary of the polygon.
    </para>

    <para>
     Polygons are output using the first syntax.
    </para>
   </sect2>

   <sect2>
    <title>Circles</title>

    <indexterm>
     <primary>circle</primary>
    </indexterm>

    <para>
     Circles are represented by a center point and a radius.
     Values of type <type>circle</type> are specified using the following syntax:

<synopsis>
&lt; ( <replaceable>x</replaceable> , <replaceable>y</replaceable> ) , <replaceable>r</replaceable> &gt;
( ( <replaceable>x</replaceable> , <replaceable>y</replaceable> ) , <replaceable>r</replaceable> )
  ( <replaceable>x</replaceable> , <replaceable>y</replaceable> ) , <replaceable>r</replaceable>  
    <replaceable>x</replaceable> , <replaceable>y</replaceable>   , <replaceable>r</replaceable>  
</synopsis>

     where
     <literal>(<replaceable>x</replaceable>,<replaceable>y</replaceable>)</literal>
     is the center and <replaceable>r</replaceable> is the radius of the circle.
    </para>

    <para>
     Circles are output using the first syntax.
    </para>
   </sect2>

  </sect1>

  <sect1 id="datatype-net-types">
   <title>Network Address Types</title>

   <indexterm zone="datatype-net-types">
    <primary>network</primary>
    <secondary>data types</secondary>
   </indexterm>

   <para>
    <productname>PostgreSQL</> offers data types to store IPv4, IPv6, and MAC
    addresses, shown in <xref linkend="datatype-net-types-table">.  It
    is preferable to use these types over plain text types, because
    these types offer input error checking and several specialized
    operators and functions.
   </para>

    <table tocentry="1" id="datatype-net-types-table">
     <title>Network Address Types</title>
     <tgroup cols="3">
      <thead>
       <row>
        <entry>Name</entry>
        <entry>Storage Size</entry>
        <entry>Description</entry>
       </row>
      </thead>
      <tbody>

       <row>
        <entry><type>cidr</type></entry>
        <entry>12 or 24 bytes</entry>
        <entry>IPv4 or IPv6 networks</entry>
       </row>

       <row>
        <entry><type>inet</type></entry>
        <entry>12 or 24 bytes</entry>
        <entry>IPv4 and IPv6 hosts and networks</entry>
       </row>

       <row>
        <entry><type>macaddr</type></entry>
        <entry>6 bytes</entry>
        <entry>MAC addresses</entry>
       </row>

      </tbody>
     </tgroup>
    </table>

   <para>
    When sorting <type>inet</type> or <type>cidr</type> data types,
    IPv4 addresses will always sort before IPv6 addresses, including
    IPv4 addresses encapsulated or mapped into IPv6 addresses, such as
    ::10.2.3.4 or ::ffff::10.4.3.2.
   </para>


   <sect2 id="datatype-inet">
    <title><type>inet</type></title>

    <indexterm>
     <primary>inet (data type)</primary>
    </indexterm>

    <para>
     The <type>inet</type> type holds an IPv4 or IPv6 host address, and
     optionally the identity of the subnet it is in, all in one field.
     The subnet identity is represented by stating how many bits of
     the host address represent the network address (the
     <quote>netmask</quote>).  If the netmask is 32 and the address is IPv4,
     then the value does not indicate a subnet, only a single host.
     In IPv6, the address length is 128 bits, so 128 bits will specify a
     unique host address.  Note that if you
     want to accept networks only, you should use the
     <type>cidr</type> type rather than <type>inet</type>.
    </para>

    <para>
      The input format for this type is
      <replaceable class="parameter">address/y</replaceable>
      where
      <replaceable class="parameter">address</replaceable>
      is an IPv4 or IPv6 address and
      <replaceable class="parameter">y</replaceable>
      is the number of bits in the netmask.  If the
      <replaceable class="parameter">/y</replaceable>
      part is left off, then the
      netmask is 32 for IPv4 and 128 for IPv6, and the value represents
      just a single host.  On display, the
      <replaceable class="parameter">/y</replaceable>
      portion is suppressed if the netmask specifies a single host.
    </para>
   </sect2>

   <sect2 id="datatype-cidr">
    <title><type>cidr</></title>

    <indexterm>
     <primary>cidr</primary>
    </indexterm>

    <para>
     The <type>cidr</type> type holds an IPv4 or IPv6 network specification.
     Input and output formats follow Classless Internet Domain Routing
     conventions.
     The format for specifying networks is <replaceable
     class="parameter">address/y</> where <replaceable
     class="parameter">address</> is the network represented as an
     IPv4 or IPv6 address, and <replaceable
     class="parameter">y</> is the number of bits in the netmask.  If
     <replaceable class="parameter">y</> is omitted, it is calculated
     using assumptions from the older classful network numbering system, except
     that it will be at least large enough to include all of the octets
     written in the input.  It is an error to specify a network address
     that has bits set to the right of the specified netmask.
    </para>

    <para>
     <xref linkend="datatype-net-cidr-table"> shows some examples.
    </para>

     <table id="datatype-net-cidr-table">
      <title><type>cidr</> Type Input Examples</title>
      <tgroup cols="3">
       <thead> 
        <row> 
         <entry><type>cidr</type> Input</entry>
         <entry><type>cidr</type> Output</entry>
         <entry><literal><function>abbrev</function>(<type>cidr</type>)</literal></entry>
        </row>
       </thead>
       <tbody>
        <row>
         <entry>192.168.100.128/25</entry>
         <entry>192.168.100.128/25</entry>
         <entry>192.168.100.128/25</entry>
        </row>
        <row>
         <entry>192.168/24</entry>
         <entry>192.168.0.0/24</entry>
         <entry>192.168.0/24</entry>
        </row>
        <row>
         <entry>192.168/25</entry>
         <entry>192.168.0.0/25</entry>
         <entry>192.168.0.0/25</entry>
        </row>
        <row>
         <entry>192.168.1</entry>
         <entry>192.168.1.0/24</entry>
         <entry>192.168.1/24</entry>
        </row>
        <row>
         <entry>192.168</entry>
         <entry>192.168.0.0/24</entry>
         <entry>192.168.0/24</entry>
        </row>
        <row>
         <entry>128.1</entry>
         <entry>128.1.0.0/16</entry>
         <entry>128.1/16</entry>
        </row>
        <row>
         <entry>128</entry>
         <entry>128.0.0.0/16</entry>
         <entry>128.0/16</entry>
        </row>
        <row>
         <entry>128.1.2</entry>
         <entry>128.1.2.0/24</entry>
         <entry>128.1.2/24</entry>
        </row>
        <row>
         <entry>10.1.2</entry>
         <entry>10.1.2.0/24</entry>
         <entry>10.1.2/24</entry>
        </row>
        <row>
         <entry>10.1</entry>
         <entry>10.1.0.0/16</entry>
         <entry>10.1/16</entry>
        </row>
        <row>
         <entry>10</entry>
         <entry>10.0.0.0/8</entry>
         <entry>10/8</entry>
        </row>
        <row>
         <entry>10.1.2.3/32</entry>
         <entry>10.1.2.3/32</entry>
         <entry>10.1.2.3/32</entry>
        </row>
        <row>
         <entry>2001:4f8:3:ba::/64</entry>
         <entry>2001:4f8:3:ba::/64</entry>
         <entry>2001:4f8:3:ba::/64</entry>
        </row>
        <row>
         <entry>2001:4f8:3:ba:2e0:81ff:fe22:d1f1/128</entry>
         <entry>2001:4f8:3:ba:2e0:81ff:fe22:d1f1/128</entry>
         <entry>2001:4f8:3:ba:2e0:81ff:fe22:d1f1</entry>
        </row>
        <row>
         <entry>::ffff:1.2.3.0/120</entry>
         <entry>::ffff:1.2.3.0/120</entry>
         <entry>::ffff:1.2.3/120</entry>
        </row>
        <row>
         <entry>::ffff:1.2.3.0/128</entry>
         <entry>::ffff:1.2.3.0/128</entry>
         <entry>::ffff:1.2.3.0/128</entry>
        </row>
       </tbody>
      </tgroup>
     </table>
   </sect2>

   <sect2 id="datatype-inet-vs-cidr">
    <title><type>inet</type> vs. <type>cidr</type></title>

    <para>
    The essential difference between <type>inet</type> and <type>cidr</type>
    data types is that <type>inet</type> accepts values with nonzero bits to
    the right of the netmask, whereas <type>cidr</type> does not.
    </para>

      <tip>
        <para>
        If you do not like the output format for <type>inet</type> or
        <type>cidr</type> values, try the functions <function>host</>,
        <function>text</>, and <function>abbrev</>.
        </para>
      </tip>
   </sect2>

   <sect2 id="datatype-macaddr">
    <title><type>macaddr</></>

    <indexterm>
     <primary>macaddr (data type)</primary>
    </indexterm>

    <indexterm>
     <primary>MAC address</primary>
     <see>macaddr</see>
    </indexterm>

    <para>
     The <type>macaddr</> type stores MAC addresses, i.e., Ethernet
     card hardware addresses (although MAC addresses are used for
     other purposes as well).  Input is accepted in various customary
     formats, including

     <simplelist>
      <member><literal>'08002b:010203'</></member>
      <member><literal>'08002b-010203'</></member>
      <member><literal>'0800.2b01.0203'</></member>
      <member><literal>'08-00-2b-01-02-03'</></member>
      <member><literal>'08:00:2b:01:02:03'</></member>
     </simplelist>

     which would all specify the same
     address.  Upper and lower case is accepted for the digits
     <literal>a</> through <literal>f</>.  Output is always in the
     last of the shown forms.
    </para>

    <para>
     The directory <filename class="directory">contrib/mac</filename>
     in the <productname>PostgreSQL</productname> source distribution
     contains tools that can be used to map MAC addresses to hardware
     manufacturer names.
    </para>
   </sect2>

  </sect1>

  <sect1 id="datatype-bit">
   <title>Bit String Types</title>

   <indexterm zone="datatype-bit">
    <primary>bit string</primary>
    <secondary>data type</secondary>
   </indexterm>

   <para>
    Bit strings are strings of 1's and 0's.  They can be used to store
    or visualize bit masks.  There are two SQL bit types:
    <type>bit(<replaceable>n</replaceable>)</type> and <type>bit
    varying(<replaceable>n</replaceable>)</type>, where
    <replaceable>n</replaceable> is a positive integer.
   </para>

   <para>
    <type>bit</type> type data must match the length
    <replaceable>n</replaceable> exactly; it is an error to attempt to
    store shorter or longer bit strings.  <type>bit varying</type> data is
    of variable length up to the maximum length
    <replaceable>n</replaceable>; longer strings will be rejected.
    Writing <type>bit</type> without a length is equivalent to
    <literal>bit(1)</literal>, while <type>bit varying</type> without a length
    specification means unlimited length.
   </para>

   <note>
    <para>
     If one explicitly casts a bit-string value to
     <type>bit(<replaceable>n</>)</type>, it will be truncated or
     zero-padded on the right to be exactly <replaceable>n</> bits,
     without raising an error.  Similarly,
     if one explicitly casts a bit-string value to
     <type>bit varying(<replaceable>n</>)</type>, it will be truncated
     on the right if it is more than <replaceable>n</> bits.
    </para>
   </note>

   <note>
    <para>
     Prior to <productname>PostgreSQL</> 7.2, <type>bit</type> data
     was always silently truncated or zero-padded on the right, with
     or without an explicit cast. This was changed to comply with the
     <acronym>SQL</acronym> standard.
    </para>
   </note>

   <para>
    Refer to <xref
    linkend="sql-syntax-bit-strings"> for information about the syntax
    of bit string constants.  Bit-logical operators and string
    manipulation functions are available; see <xref
    linkend="functions">.
   </para>

   <example>
    <title>Using the bit string types</title>

<programlisting>
CREATE TABLE test (a BIT(3), b BIT VARYING(5));
INSERT INTO test VALUES (B'101', B'00');
INSERT INTO test VALUES (B'10', B'101');
<computeroutput>
ERROR:  bit string length 2 does not match type bit(3)
</computeroutput>
INSERT INTO test VALUES (B'10'::bit(3), B'101');
SELECT * FROM test;
<computeroutput>
  a  |  b
-----+-----
 101 | 00
 100 | 101
</computeroutput>
</programlisting>
   </example>

  </sect1>

  &array;

  <sect1 id="datatype-oid">
   <title>Object Identifier Types</title>

   <indexterm zone="datatype-oid">
    <primary>object identifier</primary>
    <secondary>data type</secondary>
   </indexterm>

   <indexterm zone="datatype-oid">
    <primary>oid</primary>
   </indexterm>

   <indexterm zone="datatype-oid">
    <primary>regproc</primary>
   </indexterm>

   <indexterm zone="datatype-oid">
    <primary>regprocedure</primary>
   </indexterm>

   <indexterm zone="datatype-oid">
    <primary>regoper</primary>
   </indexterm>

   <indexterm zone="datatype-oid">
    <primary>regoperator</primary>
   </indexterm>

   <indexterm zone="datatype-oid">
    <primary>regclass</primary>
   </indexterm>

   <indexterm zone="datatype-oid">
    <primary>regtype</primary>
   </indexterm>

   <indexterm zone="datatype-oid">
    <primary>xid</primary>
   </indexterm>

   <indexterm zone="datatype-oid">
    <primary>cid</primary>
   </indexterm>

   <indexterm zone="datatype-oid">
    <primary>tid</primary>
   </indexterm>

   <para>
    Object identifiers (OIDs) are used internally by
    <productname>PostgreSQL</productname> as primary keys for various
    system tables.  An OID system column is also added to user-created
    tables, unless <literal>WITHOUT OIDS</literal> is specified when
    the table is created, or the <varname>default_with_oids</varname>
    configuration variable is set to false.  Type <type>oid</>
    represents an object identifier.  There are also several alias
    types for <type>oid</>: <type>regproc</>, <type>regprocedure</>,
    <type>regoper</>, <type>regoperator</>, <type>regclass</>, and
    <type>regtype</>. <xref linkend="datatype-oid-table"> shows an
    overview.
   </para>

   <para>
    The <type>oid</> type is currently implemented as an unsigned
    four-byte integer.  Therefore, it is not large enough to provide
    database-wide uniqueness in large databases, or even in large
    individual tables.  So, using a user-created table's OID column as
    a primary key is discouraged.  OIDs are best used only for
    references to system tables.
   </para>

   <note>
    <para>
     OIDs are included by default in user-created tables in
     <productname>PostgreSQL</productname> &version;. However, this
     behavior is likely to change in a future version of
     <productname>PostgreSQL</productname>. Eventually, user-created
     tables will not include an OID system column unless <literal>WITH
     OIDS</literal> is specified when the table is created, or the
     <varname>default_with_oids</varname> configuration variable is set
     to true. If your application requires the presence of an OID
     system column in a table, it should specify <literal>WITH
     OIDS</literal> when that table is created to ensure compatibility
     with future releases of <productname>PostgreSQL</productname>.
    </para>
   </note>

   <para>
    The <type>oid</> type itself has few operations beyond comparison.
    It can be cast to
    integer, however, and then manipulated using the standard integer
    operators.  (Beware of possible signed-versus-unsigned confusion
    if you do this.)
   </para>

   <para>
    The OID alias types have no operations of their own except
    for specialized input and output routines.  These routines are able
    to accept and display symbolic names for system objects, rather than
    the raw numeric value that type <type>oid</> would use.  The alias
    types allow simplified lookup of OID values for objects: for example,
    one may write <literal>'mytable'::regclass</> to get the OID of table
    <literal>mytable</>, rather than <literal>SELECT oid FROM pg_class WHERE
    relname = 'mytable'</>.  (In reality, a much more complicated <command>SELECT</> would
    be needed to deal with selecting the right OID when there are multiple
    tables named <literal>mytable</> in different schemas.)
   </para>

    <table id="datatype-oid-table">
     <title>Object Identifier Types</title>
     <tgroup cols="4">
      <thead>
       <row>
        <entry>Name</entry>
        <entry>References</entry>
        <entry>Description</entry>
        <entry>Value Example</entry>
       </row>
      </thead>

      <tbody>

       <row>
        <entry><type>oid</></entry>
        <entry>any</entry>
        <entry>numeric object identifier</entry>
        <entry><literal>564182</></entry>
       </row>

       <row>
        <entry><type>regproc</></entry>
        <entry><structname>pg_proc</></entry>
        <entry>function name</entry>
        <entry><literal>sum</></entry>
       </row>

       <row>
        <entry><type>regprocedure</></entry>
        <entry><structname>pg_proc</></entry>
        <entry>function with argument types</entry>
        <entry><literal>sum(int4)</></entry>
       </row>

       <row>
        <entry><type>regoper</></entry>
        <entry><structname>pg_operator</></entry>
        <entry>operator name</entry>
        <entry><literal>+</></entry>
       </row>

       <row>
        <entry><type>regoperator</></entry>
        <entry><structname>pg_operator</></entry>
        <entry>operator with argument types</entry>
        <entry><literal>*(integer,integer)</> or <literal>-(NONE,integer)</></entry>
       </row>

       <row>
        <entry><type>regclass</></entry>
        <entry><structname>pg_class</></entry>
        <entry>relation name</entry>
        <entry><literal>pg_type</></entry>
       </row>

       <row>
        <entry><type>regtype</></entry>
        <entry><structname>pg_type</></entry>
        <entry>data type name</entry>
        <entry><literal>integer</></entry>
       </row>
      </tbody>
     </tgroup>
    </table>

   <para>
    All of the OID alias types accept schema-qualified names, and will
    display schema-qualified names on output if the object would not
    be found in the current search path without being qualified.
    The <type>regproc</> and <type>regoper</> alias types will only
    accept input names that are unique (not overloaded), so they are
    of limited use; for most uses <type>regprocedure</> or
    <type>regoperator</> is more appropriate.  For <type>regoperator</>,
    unary operators are identified by writing <literal>NONE</> for the unused
    operand.
   </para>

   <para>
    Another identifier type used by the system is <type>xid</>, or transaction
    (abbreviated <abbrev>xact</>) identifier.  This is the data type of the system columns
    <structfield>xmin</> and <structfield>xmax</>.  Transaction identifiers are 32-bit quantities.
   </para>

   <para>
    A third identifier type used by the system is <type>cid</>, or
    command identifier.  This is the data type of the system columns
    <structfield>cmin</> and <structfield>cmax</>. Command identifiers are also 32-bit quantities.
   </para>

   <para>
    A final identifier type used by the system is <type>tid</>, or tuple
    identifier (row identifier).  This is the data type of the system column
    <structfield>ctid</>.  A tuple ID is a pair
    (block number, tuple index within block) that identifies the
    physical location of the row within its table.
   </para>

   <para>
    (The system columns are further explained in <xref
    linkend="ddl-system-columns">.)
   </para>
  </sect1>

  <sect1 id="datatype-pseudo">
   <title>Pseudo-Types</title>

   <indexterm zone="datatype-pseudo">
    <primary>record</primary>
   </indexterm>

   <indexterm zone="datatype-pseudo">
    <primary>any</primary>
   </indexterm>

   <indexterm zone="datatype-pseudo">
    <primary>anyarray</primary>
   </indexterm>

   <indexterm zone="datatype-pseudo">
    <primary>anyelement</primary>
   </indexterm>

   <indexterm zone="datatype-pseudo">
    <primary>void</primary>
   </indexterm>

   <indexterm zone="datatype-pseudo">
    <primary>trigger</primary>
   </indexterm>

   <indexterm zone="datatype-pseudo">
    <primary>language_handler</primary>
   </indexterm>

   <indexterm zone="datatype-pseudo">
    <primary>cstring</primary>
   </indexterm>

   <indexterm zone="datatype-pseudo">
    <primary>internal</primary>
   </indexterm>

   <indexterm zone="datatype-pseudo">
    <primary>opaque</primary>
   </indexterm>

   <para>
    The <productname>PostgreSQL</productname> type system contains a
    number of special-purpose entries that are collectively called
    <firstterm>pseudo-types</>.  A pseudo-type cannot be used as a
    column data type, but it can be used to declare a function's
    argument or result type.  Each of the available pseudo-types is
    useful in situations where a function's behavior does not
    correspond to simply taking or returning a value of a specific
    <acronym>SQL</acronym> data type.  <xref
    linkend="datatype-pseudotypes-table"> lists the existing
    pseudo-types.
   </para>

    <table id="datatype-pseudotypes-table">
     <title>Pseudo-Types</title>
     <tgroup cols="2">
      <thead>
       <row>
        <entry>Name</entry>
        <entry>Description</entry>
       </row>
      </thead>

      <tbody>
       <row>
        <entry><type>any</></entry>
        <entry>Indicates that a function accepts any input data type whatever.</entry>
       </row>

       <row>
        <entry><type>anyarray</></entry>
        <entry>Indicates that a function accepts any array data type
        (see <xref linkend="extend-types-polymorphic">).</entry>
       </row>

       <row>
        <entry><type>anyelement</></entry>
        <entry>Indicates that a function accepts any data type
        (see <xref linkend="extend-types-polymorphic">).</entry>
       </row>

       <row>
        <entry><type>cstring</></entry>
        <entry>Indicates that a function accepts or returns a null-terminated C string.</entry>
       </row>

       <row>
        <entry><type>internal</></entry>
        <entry>Indicates that a function accepts or returns a server-internal
        data type.</entry>
       </row>

       <row>
        <entry><type>language_handler</></entry>
        <entry>A procedural language call handler is declared to return <type>language_handler</>.</entry>
       </row>

       <row>
        <entry><type>record</></entry>
        <entry>Identifies a function returning an unspecified row type.</entry>
       </row>

       <row>
        <entry><type>trigger</></entry>
        <entry>A trigger function is declared to return <type>trigger.</></entry>
       </row>

       <row>
        <entry><type>void</></entry>
        <entry>Indicates that a function returns no value.</entry>
       </row>

       <row>
        <entry><type>opaque</></entry>
        <entry>An obsolete type name that formerly served all the above purposes.</entry>
       </row>
      </tbody>
     </tgroup>
    </table>

   <para>
    Functions coded in C (whether built-in or dynamically loaded) may be
    declared to accept or return any of these pseudo data types.  It is up to
    the function author to ensure that the function will behave safely
    when a pseudo-type is used as an argument type.
   </para>

   <para>
    Functions coded in procedural languages may use pseudo-types only as
    allowed by their implementation languages.  At present the procedural
    languages all forbid use of a pseudo-type as argument type, and allow
    only <type>void</> and <type>record</> as a result type (plus
    <type>trigger</> when the function is used as a trigger).  Some also
    support polymorphic functions using the types <type>anyarray</> and
    <type>anyelement</>.
   </para>

   <para>
    The <type>internal</> pseudo-type is used to declare functions
    that are meant only to be called internally by the database
    system, and not by direct invocation in a <acronym>SQL</acronym>
    query.  If a function has at least one <type>internal</>-type
    argument then it cannot be called from <acronym>SQL</acronym>.  To
    preserve the type safety of this restriction it is important to
    follow this coding rule: do not create any function that is
    declared to return <type>internal</> unless it has at least one
    <type>internal</> argument.
   </para>

  </sect1>

 </chapter>

<!-- Keep this comment at the end of the file
Local variables:
mode:sgml
sgml-omittag:nil
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-tabs-mode:nil
sgml-indent-data:t
sgml-parent-document:nil
sgml-default-dtd-file:"./reference.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:("/usr/share/sgml/catalog")
sgml-local-ecat-files:nil
End:
-->