PostgreSQL uses an internal heuristic parser for all date/time input support. Dates and times are input as strings, and are broken up into distinct fields with a preliminary determination of what kind of information may be in the field. Each field is interpreted and either assigned a numeric value, ignored, or rejected. The parser contains internal lookup tables for all textual fields, including months, days of the week, and time zones. This appendix includes information on the content of these lookup tables and describes the steps used by the parser to decode dates and times. The date/time type inputs are all decoded using the following procedure. 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 still not found, throw an error. When the token is a number or number field: If there are eight or six digits, and if no other date fields have been previously read, then interpret as a concatenated date (e.g., 19990118 or 990118). The interpretation is YYYYMMDD or YYMMDD. If the token is three digits and a year has already been read, then interpret as day of year. If four or six digits and a year has already been read, then interpret as a time (HHMM or HHMMSS). If three or more digits and no date fields have yet been found, interpret as a year (this forces yy-mm-dd ordering of the remaining date fields). Otherwise the date field ordering is assumed to follow the DateStyle setting: mm-dd-yy, dd-mm-yy, or yy-mm-dd. Throw an error if a month or day field is found to be out of range. 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 1 BC becomes year zero.) If BC was not specified, and if the year field was two digits in length, then adjust the year to four digits. If the field is less than 70, then add 2000, otherwise add 1900. Gregorian years AD 1-99 may be entered by using 4 digits with leading zeros (e.g., 0099 is AD 99). 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. shows the tokens that are permissible as abbreviations for the names of the month. Month Abbreviations April Apr August Aug December Dec February Feb January Jan July Jul June Jun March Mar November Nov October Oct September Sep, Sept The month May has no explicit abbreviation, for obvious reasons. shows the tokens that are permissible as abbreviations for the names of the days of the week. Day Abbreviation Sunday Sun Monday Mon Tuesday Tue, Tues Wednesday Wed, Weds Thursday Thu, Thur, Thurs Friday Fri Saturday Sat shows the tokens that serve various modifier purposes. Identifier Description ABSTIME Key word ignored AM Time is before 12:00 AT Key word ignored JULIAN, JD, J Next field is Julian Day ON Key word ignored PM Time is on or after 12:00 T Next field is time The key word ABSTIME is ignored for historical reasons: In very old releases of PostgreSQL, invalid values of type abstime were emitted as Invalid Abstime. This is no longer the case however and this key word will likely be dropped in a future release. time zone input abbreviations shows the time zone abbreviations recognized by PostgreSQL in date/time input values. Note that these names are not used for date/time output — display is driven by the currently selected parameter setting. (It is likely that future releases will make some use of timezone for input as well.) The table 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. Time Zone Offset from UTC Description NZDT +13:00 New Zealand Daylight-Saving 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-Saving Time SADT +10:30 South Australian Daylight-Saving Time AEST +10:00 Australia Eastern Standard Time EAST +10:00 East Australian Standard Time GST +10:00 Guam Standard Time, Russia 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, Russia zone 8 KST +09:00 Korea Standard Time MHT +09:00 Kwajalein Time WDT +09:00 West Australian Daylight-Saving 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-Saving 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 MMT +06:30 Myanmar 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 Afghanistan Time EAST +04:00 Antananarivo Summer Time MUT +04:00 Mauritius Island Time RET +04:00 Reunion Island Time SCT +04:00 Mahe Island Time IRT, IT +03:30 Iran Time EAT +03:00 Antananarivo, Comoro Time BT +03:00 Baghdad Time EETDST +03:00 Eastern Europe Daylight-Saving Time HMT +03:00 Hellas Mediterranean Time (?) BDST +02:00 British Double Summer Time CEST +02:00 Central European Summer Time CETDST +02:00 Central European Daylight-Saving Time EET +02:00 Eastern European Time, Russia zone 1 FWT +02:00 French Winter Time IST +02:00 Israel Standard Time MEST +02:00 Middle European Summer Time METDST +02:00 Middle Europe Daylight-Saving 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 European Time MEWT +01:00 Middle European Winter Time MEZ +01:00 Mitteleuropäische Zeit NOR +01:00 Norway Standard Time SET +01:00 Seychelles Time SWT +01:00 Swedish Winter Time WETDST +01:00 Western European Daylight-Saving Time GMT 00:00 Greenwich Mean Time UT 00:00 Universal Time UTC 00:00 Universal Coordinated Time Z 00:00 Same as UTC ZULU 00:00 Same as UTC WET 00:00 Western European Time WAT -01:00 West Africa Time FNST -01:00 Fernando de Noronha Summer Time FNT -02:00 Fernando de Noronha Time BRST -02:00 Brasilia Summer Time NDT -02:30 Newfoundland Daylight-Saving Time ADT -03:00 Atlantic Daylight-Saving Time AWT -03:00 (unknown) BRT -03:00 Brasilia Time 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 EDT -04:00 Eastern Daylight-Saving Time ACT -05:00 Atlantic/Porto Acre Standard Time CDT -05:00 Central Daylight-Saving Time EST -05:00 Eastern Standard Time CST -06:00 Central Standard Time MDT -06:00 Mountain Daylight-Saving Time MST -07:00 Mountain Standard Time PDT -07:00 Pacific Daylight-Saving Time AKDT -08:00 Alaska Daylight-Saving Time PST -08:00 Pacific Standard Time YDT -08:00 Yukon Daylight-Saving Time AKST -09:00 Alaska Standard Time HDT -09:00 Hawaii/Alaska Daylight-Saving Time YST -09:00 Yukon Standard Time MART -09:30 Marquesas 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 There are three naming conflicts between Australian time zone names and time zone names commonly used in North and South America: ACST, CST, and EST. If the run-time option australian_timezones is set to true then ACST, CST, EST, and SAT are interpreted as Australian time zone names, as shown in . If it is false (which is the default), then ACST, CST, and EST are taken as American time zone names, and SAT is interpreted as a noise word indicating Saturday. 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 time zone configuration names shows the time zone names recognized by PostgreSQL as valid settings for the parameter. Note that these names are conceptually as well as practically different from the names shown in : most of these names imply a local daylight-savings time rule, whereas the former names each represent just a fixed offset from UTC. In many cases there are several equivalent names for the same zone. These are listed on the same line. The table is primarily sorted by the name of the principal city of the zone. Time Zone Africa/Abidjan Africa/Accra Africa/Addis_Ababa Africa/Algiers Africa/Asmera Africa/Bamako Africa/Bangui Africa/Banjul Africa/Bissau Africa/Blantyre Africa/Brazzaville Africa/Bujumbura Africa/Cairo Egypt Africa/Casablanca Africa/Ceuta Africa/Conakry Africa/Dakar Africa/Dar_es_Salaam Africa/Djibouti Africa/Douala Africa/El_Aaiun Africa/Freetown Africa/Gaborone Africa/Harare Africa/Johannesburg Africa/Kampala Africa/Khartoum Africa/Kigali Africa/Kinshasa Africa/Lagos Africa/Libreville Africa/Lome Africa/Luanda Africa/Lubumbashi Africa/Lusaka Africa/Malabo Africa/Maputo Africa/Maseru Africa/Mbabane Africa/Mogadishu Africa/Monrovia Africa/Nairobi Africa/Ndjamena Africa/Niamey Africa/Nouakchott Africa/Ouagadougou Africa/Porto-Novo Africa/Sao_Tome Africa/Timbuktu Africa/Tripoli Libya Africa/Tunis Africa/Windhoek America/Adak America/Atka US/Aleutian America/Anchorage SystemV/YST9YDT US/Alaska America/Anguilla America/Antigua America/Araguaina America/Aruba America/Asuncion America/Bahia America/Barbados America/Belem America/Belize America/Boa_Vista America/Bogota America/Boise America/Buenos_Aires America/Cambridge_Bay America/Campo_Grande America/Cancun America/Caracas America/Catamarca America/Cayenne America/Cayman America/Chicago CST6CDT SystemV/CST6CDT US/Central America/Chihuahua America/Cordoba America/Rosario America/Costa_Rica America/Cuiaba America/Curacao America/Danmarkshavn America/Dawson America/Dawson_Creek America/Denver MST7MDT SystemV/MST7MDT US/Mountain America/Shiprock Navajo America/Detroit US/Michigan America/Dominica America/Edmonton Canada/Mountain America/Eirunepe America/El_Salvador America/Ensenada America/Tijuana Mexico/BajaNorte America/Fortaleza America/Glace_Bay America/Godthab America/Goose_Bay America/Grand_Turk America/Grenada America/Guadeloupe America/Guatemala America/Guayaquil America/Guyana America/Halifax Canada/Atlantic SystemV/AST4ADT America/Havana Cuba America/Hermosillo America/Indiana/Indianapolis America/Indianapolis America/Fort_Wayne EST SystemV/EST5 US/East-Indiana America/Indiana/Knox America/Knox_IN US/Indiana-Starke America/Indiana/Marengo America/Indiana/Vevay America/Inuvik America/Iqaluit America/Jamaica Jamaica America/Jujuy America/Juneau America/Kentucky/Louisville America/Louisville America/Kentucky/Monticello America/La_Paz America/Lima America/Los_Angeles PST8PDT SystemV/PST8PDT US/Pacific US/Pacific-New America/Maceio America/Managua America/Manaus Brazil/West America/Martinique America/Mazatlan Mexico/BajaSur America/Mendoza America/Menominee America/Merida America/Mexico_City Mexico/General America/Miquelon America/Monterrey America/Montevideo America/Montreal America/Montserrat America/Nassau America/New_York EST5EDT SystemV/EST5EDT US/Eastern America/Nipigon America/Nome America/Noronha Brazil/DeNoronha America/North_Dakota/Center America/Panama America/Pangnirtung America/Paramaribo America/Phoenix MST SystemV/MST7 US/Arizona America/Port-au-Prince America/Port_of_Spain America/Porto_Acre America/Rio_Branco Brazil/Acre America/Porto_Velho America/Puerto_Rico SystemV/AST4 America/Rainy_River America/Rankin_Inlet America/Recife America/Regina Canada/East-Saskatchewan Canada/Saskatchewan SystemV/CST6 America/Santiago Chile/Continental America/Santo_Domingo America/Sao_Paulo Brazil/East America/Scoresbysund America/St_Johns Canada/Newfoundland America/St_Kitts America/St_Lucia America/St_Thomas America/Virgin America/St_Vincent America/Swift_Current America/Tegucigalpa America/Thule America/Thunder_Bay America/Toronto Canada/Eastern America/Tortola America/Vancouver Canada/Pacific America/Whitehorse Canada/Yukon America/Winnipeg Canada/Central America/Yakutat America/Yellowknife Antarctica/Casey Antarctica/Davis Antarctica/DumontDUrville Antarctica/Mawson Antarctica/McMurdo Antarctica/South_Pole Antarctica/Palmer Antarctica/Rothera Antarctica/Syowa Antarctica/Vostok Asia/Aden Asia/Almaty Asia/Amman Asia/Anadyr Asia/Aqtau Asia/Aqtobe Asia/Ashgabat Asia/Ashkhabad Asia/Baghdad Asia/Bahrain Asia/Baku Asia/Bangkok Asia/Beirut Asia/Bishkek Asia/Brunei Asia/Calcutta Asia/Choibalsan Asia/Chongqing Asia/Chungking Asia/Colombo Asia/Dacca Asia/Dhaka Asia/Damascus Asia/Dili Asia/Dubai Asia/Dushanbe Asia/Gaza Asia/Harbin Asia/Hong_Kong Hongkong Asia/Hovd Asia/Irkutsk Asia/Jakarta Asia/Jayapura Asia/Jerusalem Asia/Tel_Aviv Israel Asia/Kabul Asia/Kamchatka Asia/Karachi Asia/Kashgar Asia/Katmandu Asia/Krasnoyarsk Asia/Kuala_Lumpur Asia/Kuching Asia/Kuwait Asia/Macao Asia/Macau Asia/Magadan Asia/Makassar Asia/Ujung_Pandang Asia/Manila Asia/Muscat Asia/Nicosia Europe/Nicosia Asia/Novosibirsk Asia/Omsk Asia/Oral Asia/Phnom_Penh Asia/Pontianak Asia/Pyongyang Asia/Qatar Asia/Qyzylorda Asia/Rangoon Asia/Riyadh Asia/Riyadh87 Mideast/Riyadh87 Asia/Riyadh88 Mideast/Riyadh88 Asia/Riyadh89 Mideast/Riyadh89 Asia/Saigon Asia/Sakhalin Asia/Samarkand Asia/Seoul ROK Asia/Shanghai PRC Asia/Singapore Singapore Asia/Taipei ROC Asia/Tashkent Asia/Tbilisi Asia/Tehran Iran Asia/Thimbu Asia/Thimphu Asia/Tokyo Japan Asia/Ulaanbaatar Asia/Ulan_Bator Asia/Urumqi Asia/Vientiane Asia/Vladivostok Asia/Yakutsk Asia/Yekaterinburg Asia/Yerevan Atlantic/Azores Atlantic/Bermuda Atlantic/Canary Atlantic/Cape_Verde Atlantic/Faeroe Atlantic/Madeira Atlantic/Reykjavik Iceland Atlantic/South_Georgia Atlantic/St_Helena Atlantic/Stanley Australia/ACT Australia/Canberra Australia/NSW Australia/Sydney Australia/Adelaide Australia/South Australia/Brisbane Australia/Queensland Australia/Broken_Hill Australia/Yancowinna Australia/Darwin Australia/North Australia/Hobart Australia/Tasmania Australia/LHI Australia/Lord_Howe Australia/Lindeman Australia/Melbourne Australia/Victoria Australia/Perth Australia/West CET EET Etc/GMT+1 Etc/GMT+2 Etc/GMT+3 Etc/GMT+4 Etc/GMT+5 Etc/GMT+6 Etc/GMT+7 Etc/GMT+8 Etc/GMT+9 Etc/GMT+10 Etc/GMT+11 Etc/GMT+12 Etc/GMT-1 Etc/GMT-2 Etc/GMT-3 Etc/GMT-4 Etc/GMT-5 Etc/GMT-6 Etc/GMT-7 Etc/GMT-8 Etc/GMT-9 Etc/GMT-10 Etc/GMT-11 Etc/GMT-12 Etc/GMT-13 Etc/GMT-14 Europe/Amsterdam Europe/Andorra Europe/Athens Europe/Belfast Europe/Belgrade Europe/Ljubljana Europe/Sarajevo Europe/Skopje Europe/Zagreb Europe/Berlin Europe/Brussels Europe/Bucharest Europe/Budapest Europe/Chisinau Europe/Tiraspol Europe/Copenhagen Europe/Dublin Eire Europe/Gibraltar Europe/Helsinki Europe/Istanbul Asia/Istanbul Turkey Europe/Kaliningrad Europe/Kiev Europe/Lisbon Portugal Europe/London GB GB-Eire Europe/Luxembourg Europe/Madrid Europe/Malta Europe/Minsk Europe/Monaco Europe/Moscow W-SU Europe/Oslo Arctic/Longyearbyen Atlantic/Jan_Mayen Europe/Paris Europe/Prague Europe/Bratislava Europe/Riga Europe/Rome Europe/San_Marino Europe/Vatican Europe/Samara Europe/Simferopol Europe/Sofia Europe/Stockholm Europe/Tallinn Europe/Tirane Europe/Uzhgorod Europe/Vaduz Europe/Vienna Europe/Vilnius Europe/Warsaw Poland Europe/Zaporozhye Europe/Zurich Factory GMT GMT+0 GMT-0 GMT0 Greenwich Etc/GMT Etc/GMT+0 Etc/GMT-0 Etc/GMT0 Etc/Greenwich Indian/Antananarivo Indian/Chagos Indian/Christmas Indian/Cocos Indian/Comoro Indian/Kerguelen Indian/Mahe Indian/Maldives Indian/Mauritius Indian/Mayotte Indian/Reunion MET Pacific/Apia Pacific/Auckland NZ Pacific/Chatham NZ-CHAT Pacific/Easter Chile/EasterIsland Pacific/Efate Pacific/Enderbury Pacific/Fakaofo Pacific/Fiji Pacific/Funafuti Pacific/Galapagos Pacific/Gambier SystemV/YST9 Pacific/Guadalcanal Pacific/Guam Pacific/Honolulu HST SystemV/HST10 US/Hawaii Pacific/Johnston Pacific/Kiritimati Pacific/Kosrae Pacific/Kwajalein Kwajalein Pacific/Majuro Pacific/Marquesas Pacific/Midway Pacific/Nauru Pacific/Niue Pacific/Norfolk Pacific/Noumea Pacific/Pago_Pago Pacific/Samoa US/Samoa Pacific/Palau Pacific/Pitcairn SystemV/PST8 Pacific/Ponape Pacific/Port_Moresby Pacific/Rarotonga Pacific/Saipan Pacific/Tahiti Pacific/Tarawa Pacific/Tongatapu Pacific/Truk Pacific/Wake Pacific/Wallis Pacific/Yap UCT Etc/UCT UTC Universal Zulu Etc/UTC Etc/Universal Etc/Zulu WET In addition to the names listed in the table, PostgreSQL will accept time zone names of the form STDoffset or STDoffsetDST, where STD is a zone abbreviation, offset is a numeric offset in hours west from UTC, and DST is an optional daylight-savings zone abbreviation, assumed to stand for one hour ahead of the given offset. For example, if EST5EDT were not already a recognized zone name, it would be accepted and would be functionally equivalent to USA East Coast time. When a daylight-savings zone name is present, it is assumed to be used according to USA time zone rules, so this feature is of limited use outside North America. One should also be wary that this provision can lead to silently accepting bogus input, since there is no check on the reasonableness of the zone abbreviations. For example, SET TIMEZONE TO FOOBAR0 will work, leaving the system effectively using a rather peculiar abbreviation for GMT. The Julian Date was invented by the French scholar Joseph Justus Scaliger (1540-1609) and probably takes its name from Scaliger's father, the Italian scholar Julius Caesar Scaliger (1484-1558). Astronomers have used the Julian period to assign a unique number to every day since 1 January 4713 BC. This is the so-called Julian Date (JD). JD 0 designates the 24 hours from noon UTC on 1 January 4713 BC to noon UTC on 2 January 4713 BC. The Julian Date is different from the Julian Calendar. The Julian calendar was introduced by Julius Caesar in 45 BC. It was in common use until the year 1582, when countries started changing to the Gregorian calendar. In the Julian calendar, the tropical year is approximated as 365 1/4 days = 365.25 days. This gives an error of about 1 day in 128 years. The accumulating calendar error prompted Pope Gregory XIII to reform the calendar in accordance with instructions from the Council of Trent. In the Gregorian calendar, the tropical year is approximated as 365 + 97 / 400 days = 365.2425 days. Thus it takes approximately 3300 years for the tropical year to shift one day with respect to the Gregorian calendar. The approximation 365+97/400 is achieved by having 97 leap years every 400 years, using the following rules: Every year divisible by 4 is a leap year. However, every year divisible by 100 is not a leap year. However, every year divisible by 400 is a leap year after all. So, 1700, 1800, 1900, 2100, and 2200 are not leap years. But 1600, 2000, and 2400 are leap years. By contrast, in the older Julian calendar all years divisible by 4 are leap years. The papal bull of February 1582 decreed that 10 days should be dropped from October 1582 so that 15 October should follow immediately after 4 October. This was observed in Italy, Poland, Portugal, and Spain. Other Catholic countries followed shortly after, but Protestant countries were reluctant to change, and the Greek orthodox countries didn't change until the start of the 20th century. The reform was observed by Great Britain and Dominions (including what is now the USA) in 1752. Thus 2 September 1752 was followed by 14 September 1752. This is why Unix systems have the cal program produce the following: $ cal 9 1752 September 1752 S M Tu W Th F S 1 2 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 The SQL standard states that Within the definition of a datetime literal, the datetime values are constrained by the natural rules for dates and times according to the Gregorian calendar. Dates between 1752-09-03 and 1752-09-13, although eliminated in some countries by Papal fiat, conform to natural rules and are hence valid dates. Different calendars have been developed in various parts of the world, many predating the Gregorian system. For example, the beginnings of the Chinese calendar can be traced back to the 14th century BC. Legend has it that the Emperor Huangdi invented the calendar in 2637 BC. The People's Republic of China uses the Gregorian calendar for civil purposes. The Chinese calendar is used for determining festivals.