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A.2. Time Zones

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

A.2.1. Australian Time Zones

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

A.2.2. Date/Time Input Interpretation

The date/time types are all decoded using a common set of routines.

Date/Time Input Interpretation

  1. Break the input string into tokens and categorize each token as a string, time, time zone, or number.

    1. If the numeric token contains a colon (":"), this is a time string. Include all subsequent digits and colons.

    2. If the numeric token contains a dash ("-"), slash ("/"), or two or more dots ("."), this is a date string which may have a text month.

    3. 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).

    4. If the token starts with a plus ("+") or minus ("-"), then it is either a time zone or a special field.

  2. If the token is a text string, match up with possible strings.

    1. 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.

    2. If not found, do a similar binary-search table lookup to match the token with a time zone.

    3. If not found, throw an error.

  3. The token is a number or number field.

    1. 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.

    2. If the token is three digits and a year has already been decoded, then interpret as day of year.

    3. If four or six digits and a year has already been read, then interpret as a time.

    4. If four or more digits, then interpret as a year.

    5. 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.

    6. 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.

    7. 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.

    8. If two digits or four or more digits, then interpret as a year.

    9. Otherwise, throw an error.

  4. 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).

  5. 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.

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