PostgreSQL contains internal tabular information for time zone decoding, since there is no *nix standard system interface to provide access to general, cross-timezone information. The underlying OS is used to provide time zone information for output, however.
The following table of time zones recognized by PostgreSQL is organized by time zone offset from UTC, rather than alphabetically; this is intended to facilitate matching local usage with recognized abbreviations for cases where these might differ.
Table A-4. PostgreSQL Recognized Time Zones
| Time Zone | Offset from UTC | Description |
|---|---|---|
| NZDT | +13:00 | New Zealand Daylight Time |
| IDLE | +12:00 | International Date Line, East |
| NZST | +12:00 | New Zealand Standard Time |
| NZT | +12:00 | New Zealand Time |
| AESST | +11:00 | Australia Eastern Summer Standard Time |
| ACSST | +10:30 | Central Australia Summer Standard Time |
| CADT | +10:30 | Central Australia Daylight Savings Time |
| SADT | +10:30 | South Australian Daylight Time |
| AEST | +10:00 | Australia Eastern Standard Time |
| EAST | +10:00 | East Australian Standard Time |
| GST | +10:00 | Guam Standard Time, USSR Zone 9 |
| LIGT | +10:00 | Melbourne, Australia |
| SAST | +09:30 | South Australia Standard Time |
| CAST | +09:30 | Central Australia Standard Time |
| AWSST | +09:00 | Australia Western Summer Standard Time |
| JST | +09:00 | Japan Standard Time,USSR Zone 8 |
| KST | +09:00 | Korea Standard Time |
| MHT | +09:00 | Kwajalein Time |
| WDT | +09:00 | West Australian Daylight Time |
| MT | +08:30 | Moluccas Time |
| AWST | +08:00 | Australia Western Standard Time |
| CCT | +08:00 | China Coastal Time |
| WADT | +08:00 | West Australian Daylight Time |
| WST | +08:00 | West Australian Standard Time |
| JT | +07:30 | Java Time |
| ALMST | +07:00 | Almaty Summer Time |
| WAST | +07:00 | West Australian Standard Time |
| CXT | +07:00 | Christmas (Island) Time |
| ALMT | +06:00 | Almaty Time |
| MAWT | +06:00 | Mawson (Antarctica) Time |
| IOT | +05:00 | Indian Chagos Time |
| MVT | +05:00 | Maldives Island Time |
| TFT | +05:00 | Kerguelen Time |
| AFT | +04:30 | Afganistan Time |
| EAST | +04:00 | Antananarivo Savings Time |
| MUT | +04:00 | Mauritius Island Time |
| RET | +04:00 | Reunion Island Time |
| SCT | +04:00 | Mahe Island Time |
| IT | +03:30 | Iran Time |
| EAT | +03:00 | Antananarivo, Comoro Time |
| BT | +03:00 | Baghdad Time |
| EETDST | +03:00 | Eastern Europe Daylight Savings Time |
| HMT | +03:00 | Hellas Mediterranean Time (?) |
| BDST | +02:00 | British Double Standard Time |
| CEST | +02:00 | Central European Savings Time |
| CETDST | +02:00 | Central European Daylight Savings Time |
| EET | +02:00 | Eastern Europe, USSR Zone 1 |
| FWT | +02:00 | French Winter Time |
| IST | +02:00 | Israel Standard Time |
| MEST | +02:00 | Middle Europe Summer Time |
| METDST | +02:00 | Middle Europe Daylight Time |
| SST | +02:00 | Swedish Summer Time |
| BST | +01:00 | British Summer Time |
| CET | +01:00 | Central European Time |
| DNT | +01:00 | Dansk Normal Tid |
| FST | +01:00 | French Summer Time |
| MET | +01:00 | Middle Europe Time |
| MEWT | +01:00 | Middle Europe Winter Time |
| MEZ | +01:00 | Middle Europe Zone |
| NOR | +01:00 | Norway Standard Time |
| SET | +01:00 | Seychelles Time |
| SWT | +01:00 | Swedish Winter Time |
| WETDST | +01:00 | Western Europe Daylight Savings Time |
| GMT | +00:00 | Greenwich Mean Time |
| UT | +00:00 | Universal Time |
| UTC | +00:00 | Universal Time, Coordinated |
| Z | +00:00 | Same as UTC |
| ZULU | +00:00 | Same as UTC |
| WET | +00:00 | Western Europe |
| WAT | -01:00 | West Africa Time |
| NDT | -02:30 | Newfoundland Daylight Time |
| ADT | -03:00 | Atlantic Daylight Time |
| AWT | -03:00 | (unknown) |
| NFT | -03:30 | Newfoundland Standard Time |
| NST | -03:30 | Newfoundland Standard Time |
| AST | -04:00 | Atlantic Standard Time (Canada) |
| ACST | -04:00 | Atlantic/Porto Acre Summer Time |
| ACT | -05:00 | Atlantic/Porto Acre Standard Time |
| EDT | -04:00 | Eastern Daylight Time |
| CDT | -05:00 | Central Daylight Time |
| EST | -05:00 | Eastern Standard Time |
| CST | -06:00 | Central Standard Time |
| MDT | -06:00 | Mountain Daylight Time |
| MST | -07:00 | Mountain Standard Time |
| PDT | -07:00 | Pacific Daylight Time |
| AKDT | -08:00 | Alaska Daylight Time |
| PST | -08:00 | Pacific Standard Time |
| YDT | -08:00 | Yukon Daylight Time |
| AKST | -09:00 | Alaska Standard Time |
| HDT | -09:00 | Hawaii/Alaska Daylight Time |
| YST | -09:00 | Yukon Standard Time |
| AHST | -10:00 | Alaska-Hawaii Standard Time |
| HST | -10:00 | Hawaii Standard Time |
| CAT | -10:00 | Central Alaska Time |
| NT | -11:00 | Nome Time |
| IDLW | -12:00 | International Date Line, West |
Australian time zones and their naming variants account for fully one quarter of all time zones in the PostgreSQL time zone lookup table. There are two naming conflicts with time zones commonly used in the United States, CST and EST.
If the runtime option AUSTRALIAN_TIMEZONES is set then CST, EST, and SAT will be interpreted as Australian timezone names. Without this option, CST and EST are taken as American timezone names, while SAT is interpreted as a noise word indicating Saturday.
Table A-5. PostgreSQL Australian Time Zones
| Time Zone | Offset from UTC | Description |
|---|---|---|
| ACST | +09:30 | Central Australia Standard Time |
| CST | +10:30 | Australian Central Standard Time |
| EST | +10:00 | Australian Eastern Standard Time |
| SAT | +09:30 | South Australian Standard Time |
The date/time types are all decoded using a common set of routines.
Date/Time Input Interpretation
Break the input string into tokens and categorize each token as a string, time, time zone, or number.
If the numeric token contains a colon (":"), this is a time string. Include all subsequent digits and colons.
If the numeric token contains a dash ("-"), slash ("/"), or two or more dots ("."), this is a date string which may have a text month.
If the token is numeric only, then it is either a single field or an ISO-8601 concatenated date (e.g. 19990113 for January 13, 1999) or time (e.g. 141516 for 14:15:16).
If the token starts with a plus ("+") or minus ("-"), then it is either a time zone or a special field.
If the token is a text string, match up with possible strings.
Do a binary-search table lookup for the token as either a special string (e.g. today), day (e.g. Thursday), month (e.g. January), or noise word (e.g. at, on).
Set field values and bit mask for fields. For example, set year, month, day for today, and additionally hour, minute, second for now.
If not found, do a similar binary-search table lookup to match the token with a time zone.
If not found, throw an error.
The token is a number or number field.
If there are more than 4 digits, and if no other date fields have been previously read, then interpret as a "concatenated date" (e.g. 19990118). 8 and 6 digits are interpreted as year, month, and day, while 7 and 5 digits are interpreted as year, day of year, respectively.
If the token is three digits and a year has already been decoded, then interpret as day of year.
If four or six digits and a year has already been read, then interpret as a time.
If four or more digits, then interpret as a year.
If in European date mode, and if the day field has not yet been read, and if the value is less than or equal to 31, then interpret as a day.
If the month field has not yet been read, and if the value is less than or equal to 12, then interpret as a month.
If the day field has not yet been read, and if the value is less than or equal to 31, then interpret as a day.
If two digits or four or more digits, then interpret as a year.
Otherwise, throw an error.
If BC has been specified, negate the year and add one for internal storage (there is no year zero in the Gregorian calendar, so numerically 1BC becomes year zero).
If BC was not specified, and if the year field was two digits in length, then adjust the year to 4 digits. If the field was less than 70, then add 2000; otherwise, add 1900.
Tip: Gregorian years 1-99AD may be entered by using 4 digits with leading zeros (e.g. 0099 is 99AD). Previous versions of PostgreSQL accepted years with three digits and with single digits, but as of version 7.0 the rules have been tightened up to reduce the possibility of ambiguity.