PostgreSQLsupports the full set ofSQLdate and time types, shown inTable 8.9. The operations available on these data types are described inSection 9.9. Dates are counted according to the Gregorian calendar, even in years before that calendar was introduced (seeSection B.4for more information).
Table 8.9. Date/Time Types
|Name||Storage Size||Description||Low Value||High Value||Resolution|
||8 bytes||both date and time (no time zone)||4713 BC||294276 AD||1 microsecond|
||8 bytes||both date and time, with time zone||4713 BC||294276 AD||1 microsecond|
||4 bytes||date (no time of day)||4713 BC||5874897 AD||1 day|
||8 bytes||time of day (no date)||00:00:00||24:00:00||1 microsecond|
||12 bytes||time of day (no date), with time zone||00:00:00+1459||24:00:00-1459||1 microsecond|
||16 bytes||time interval||-178000000 years||178000000 years||1 microsecond|
The SQL standard requires that writing just
timestampbe equivalent to
timestamp without time zone, andPostgreSQLhonors that behavior.
timestamptzis accepted as an abbreviation for
timestamp with time zone; this is aPostgreSQLextension.
intervalaccept an optional precision value
p_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
p_is from 0 to 6.
intervaltype has an additional option, which is to restrict the set of stored fields by writing one of these phrases:
YEAR MONTH DAY HOUR MINUTE SECOND YEAR TO MONTH DAY TO HOUR DAY TO MINUTE DAY TO SECOND HOUR TO MINUTE HOUR TO SECOND MINUTE TO SECOND
Note that if both
pare specified, the
SECOND, since the precision applies only to the seconds.
time with time zoneis defined by the SQL standard, but the definition exhibits properties which lead to questionable usefulness. In most cases, a combination of
timestamp without time zone, and
timestamp with time zoneshould provide a complete range of date/time functionality required by any application.
reltimeare lower precision types which are used internally. You are discouraged from using these types in applications; these internal types might disappear in a future release.
8.5.1. Date/Time Input
Date and time input is accepted in almost any reasonable format, including ISO 8601,SQL-compatible, traditionalPOSTGRES, and others. For some formats, ordering of day, month, and year in date input is ambiguous and there is support for specifying the expected ordering of these fields. Set theDateStyleparameter to
MDYto select month-day-year interpretation,
DMYto select day-month-year interpretation, or
YMDto select year-month-day interpretation.
PostgreSQLis more flexible in handling date/time input than theSQLstandard requires. SeeAppendix Bfor the exact parsing rules of date/time input and for the recognized text fields including months, days of the week, and time zones.
Remember that any date or time literal input needs to be enclosed in single quotes, like text strings. Refer toSection 18.104.22.168for more information.SQLrequires the following syntax
type [ ( p ) ] ' value '
p_is an optional precision specification giving the number of fractional digits in the seconds field. Precision can be specified for
intervaltypes, and can range from 0 to 6. If no precision is specified in a constant specification, it defaults to the precision of the literal value (but not more than 6 digits).
Table 8.10shows some possible inputs for the
Table 8.10. Date Input
|1999-01-08||ISO 8601; January 8 in any mode (recommended format)|
|January 8, 1999||unambiguous in any
|1/8/1999||January 8 in
|1/18/1999||January 18 in
|01/02/03||January 2, 2003 in
|1999-Jan-08||January 8 in any mode|
|Jan-08-1999||January 8 in any mode|
|08-Jan-1999||January 8 in any mode|
|99-Jan-08||January 8 in
|08-Jan-99||January 8, except error in
|Jan-08-99||January 8, except error in
|19990108||ISO 8601; January 8, 1999 in any mode|
|990108||ISO 8601; January 8, 1999 in any mode|
|1999.008||year and day of year|
|January 8, 99 BC||year 99 BC|
The time-of-day types are
time [ (
p) ] without time zoneand
time [ (
p) ] with time zone.
timealone is equivalent to
time without time zone.
Valid input for these types consists of a time of day followed by an optional time zone. (SeeTable 8.11andTable 8.12.) If a time zone is specified in the input for
time without time zone, it is silently ignored. You can also specify a date but it will be ignored, except when you use a time zone name that involves a daylight-savings rule, such as
America/New_York. In this case specifying the date is required in order to determine whether standard or daylight-savings time applies. The appropriate time zone offset is recorded in the
time with time zonevalue.
Table 8.11. Time Input
||same as 04:05; AM does not affect value|
||same as 16:05; input hour must be <= 12|
||time zone specified by abbreviation|
||time zone specified by full name|
Table 8.12. Time Zone Input
||Abbreviation (for Pacific Standard Time)|
||Full time zone name|
||POSIX-style time zone specification|
||ISO-8601 offset for PST|
||ISO-8601 offset for PST|
||ISO-8601 offset for PST|
||Military abbreviation for UTC|
||Short form of
Refer toSection 8.5.3for more information on how to specify time zones.
22.214.171.124. Time Stamps
Valid input for the time stamp types consists of the concatenation of a date and a time, followed by an optional time zone, followed by an optional
BCcan appear before the time zone, but this is not the preferred ordering.) Thus:
1999-01-08 04:05:06 -8:00
are valid values, which follow theISO8601 standard. In addition, the common format:
January 8 04:05:06 1999 PST
timestamp without time zoneand
timestamp with time zoneliterals by the presence of a“+”or“-”symbol and time zone offset after the time. Hence, according to the standard,
TIMESTAMP '2004-10-19 10:23:54'
timestamp without time zone, while
TIMESTAMP '2004-10-19 10:23:54+02'
timestamp with time zone.PostgreSQLnever examines the content of a literal string before determining its type, and therefore will treat both of the above as
timestamp without time zone. To ensure that a literal is treated as
timestamp with time zone, give it the correct explicit type:
TIMESTAMP WITH TIME ZONE '2004-10-19 10:23:54+02'
In a literal that has been determined to be
timestamp without time zone,PostgreSQLwill silently ignore any time zone indication. That is, the resulting value is derived from the date/time fields in the input value, and is not adjusted for time zone.
timestamp with time zone, the internally stored value is always in UTC (Universal Coordinated Time, traditionally known as Greenwich Mean Time,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'sTimeZoneparameter, and is converted to UTC using the offset for the
timestamp with time zonevalue is output, it is always converted from UTC to the current
timezonezone, and displayed as local time in that zone. To see the time in another time zone, either change
timezoneor use the
AT TIME ZONEconstruct (seeSection 9.9.3).
timestamp without time zoneand
timestamp with time zonenormally assume that the
timestamp without time zonevalue should be taken or given as
timezonelocal time. A different time zone can be specified for the conversion using
AT TIME ZONE.
126.96.36.199. Special Values
PostgreSQLsupports several special date/time input values for convenience, as shown inTable 8.13. The values
-infinityare specially represented inside the system and will be displayed unchanged; but the others are simply notational shorthands that will be converted to ordinary date/time values when read. (In particular,
nowand related strings are converted to a specific time value as soon as they are read.) All of these values need to be enclosed in single quotes when used as constants in SQL commands.
Table 8.13. Special Date/Time Inputs
|Input String||Valid Types||Description|
||1970-01-01 00:00:00+00 (Unix system time zero)|
||later than all other time stamps|
||earlier than all other time stamps|
||current transaction's start time|
The followingSQL-compatible functions can also be used to obtain the current time value for the corresponding data type:
LOCALTIMESTAMP. The latter four accept an optional subsecond precision specification. (SeeSection 9.9.4.) Note that these are SQL functions and are_not_recognized in data input strings.
8.5.2. Date/Time Output
The output format of the date/time types can be set to one of the four styles ISO 8601,SQL(Ingres), traditionalPOSTGRES(Unixdateformat), or German. The default is theISOformat. (TheSQLstandard requires the use of the ISO 8601 format. The name of the“SQL”output format is a historical accident.)Table 8.14shows examples of each output style. The output of the
timetypes is generally only the date or time part in accordance with the given examples. However, thePOSTGRESstyle outputs date-only values inISOformat.
Table 8.14. Date/Time Output Styles
||ISO 8601, SQL standard||
ISO 8601 specifies the use of uppercase letter
Tto separate the date and time.PostgreSQLaccepts that format on input, but on output it uses a space rather than
T, as shown above. This is for readability and for consistency with RFC 3339 as well as some other database systems.
In theSQLand POSTGRES styles, day appears before month if DMY field ordering has been specified, otherwise month appears before day. (SeeSection 8.5.1for how this setting also affects interpretation of input values.)Table 8.15shows examples.
Table 8.15. Date Order Conventions
||Setting||Input Ordering||Example Output|
The date/time style can be selected by the user using the
SET datestylecommand, theDateStyleparameter in the
postgresql.confconfiguration file, or the
PGDATESTYLEenvironment variable on the server or client.
The formatting function
to_char(seeSection 9.8) is also available as a more flexible way to format date/time output.
8.5.3. Time Zones
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 1900s, but continue to be prone to arbitrary changes, particularly with respect to daylight-savings rules.PostgreSQLuses the widely-used IANA (Olson) time zone database for information about historical time zone rules. For times in the future, the assumption is that the latest known rules for a given time zone will continue to be observed indefinitely far into the future.
PostgreSQLendeavors to be compatible with theSQLstandard definitions for typical usage. However, theSQLstandard has an odd mix of date and time types and capabilities. Two obvious problems are:
datetype cannot have an associated time zone, the
timetype can. Time zones in the real world have little meaning unless associated with a date as well as a time, since the offset can vary through the year with daylight-saving time boundaries.
The default time zone is specified as a constant numeric offset fromUTC. It is therefore impossible to adapt to daylight-saving time when doing date/time arithmetic acrossDSTboundaries.
To address these difficulties, we recommend using date/time types that contain both date and time when using time zones. We do_not_recommend using the type
time with time zone(though it is supported byPostgreSQLfor legacy applications and for compliance with theSQLstandard).PostgreSQLassumes your local time zone for any type containing only date or time.
All timezone-aware dates and times are stored internally inUTC. They are converted to local time in the zone specified by theTimeZoneconfiguration parameter before being displayed to the client.
PostgreSQLallows you to specify time zones in three different forms:
A full time zone name, for example
America/New_York. The recognized time zone names are listed in the
pg_timezone_namesview (seeSection 51.90).PostgreSQLuses the widely-used IANA time zone data for this purpose, so the same time zone names are also recognized by much other software.
A time zone abbreviation, for example
PST. Such a specification merely defines a particular offset from UTC, in contrast to full time zone names which can imply a set of daylight savings transition-date rules as well. The recognized abbreviations are listed in the
pg_timezone_abbrevsview (seeSection 51.89). You cannot set the configuration parametersTimeZoneorlog_timezoneto a time zone abbreviation, but you can use abbreviations in date/time input values and with the
AT TIME ZONEoperator.
In addition to the timezone names and abbreviations,PostgreSQLwill accept POSIX-style time zone specifications of the form
STDis a zone abbreviation,
offsetis 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
EST5EDTwere not already a recognized zone name, it would be accepted and would be functionally equivalent to United States East Coast time. In this syntax, a zone abbreviation can be a string of letters, or an arbitrary string surrounded by angle brackets (
<>). When a daylight-savings zone abbreviation is present, it is assumed to be used according to the same daylight-savings transition rules used in the IANA time zone database's
posixrulesentry. In a standardPostgreSQLinstallation,
posixrulesis the same as
US/Eastern, so that POSIX-style time zone specifications follow USA daylight-savings rules. If needed, you can adjust this behavior by replacing the
In short, this is the difference between abbreviations and full names: abbreviations represent a specific offset from UTC, whereas many of the full names imply a local daylight-savings time rule, and so have two possible UTC offsets. As an example,
2014-06-04 12:00 America/New_Yorkrepresents noon local time in New York, which for this particular date was Eastern Daylight Time (UTC-4). So
2014-06-04 12:00 EDTspecifies that same time instant. But
2014-06-04 12:00 ESTspecifies noon Eastern Standard Time (UTC-5), regardless of whether daylight savings was nominally in effect on that date.
To complicate matters, some jurisdictions have used the same timezone abbreviation to mean different UTC offsets at different times; for example, in Moscow
MSKhas meant UTC+3 in some years and UTC+4 in others.PostgreSQLinterprets such abbreviations according to whatever they meant (or had most recently meant) on the specified date; but, as with the
ESTexample above, this is not necessarily the same as local civil time on that date.
One should be wary that the POSIX-style time zone feature can lead to silently accepting bogus input, since there is no check on the reasonableness of the zone abbreviations. For example,
SET TIMEZONE TO FOOBAR0will work, leaving the system effectively using a rather peculiar abbreviation for UTC. Another issue to keep in mind is that in POSIX time zone names, positive offsets are used for locations_west_of Greenwich. Everywhere else,PostgreSQLfollows the ISO-8601 convention that positive timezone offsets are_east_of Greenwich.
In all cases, timezone names and abbreviations are recognized case-insensitively. (This is a change fromPostgreSQLversions prior to 8.2, which were case-sensitive in some contexts but not others.)
Neither timezone names nor abbreviations are hard-wired into the server; they are obtained from configuration files stored under
.../share/timezonesets/of the installation directory (seeSection B.3).
SET TIME ZONEsets the time zone for the session. This is an alternative spelling of
SET TIMEZONE TOwith a more SQL-spec-compatible syntax.
PGTZenvironment variable is used bylibpqclients to send a
SET TIME ZONEcommand to the server upon connection.
8.5.4. Interval Input
intervalvalues can be written using the following verbose syntax:
[ @ ] quantity unit [ quantity unit ... ] [ direction ]
quantity_is a number (possibly signed);
millennium, or abbreviations or plurals of these units;
agoor empty. The at sign (
@) is optional noise. The amounts of the different units are implicitly added with appropriate sign accounting.
agonegates all the fields. This syntax is also used for interval output, ifIntervalStyleis set to
Quantities of days, hours, minutes, and seconds can be specified without explicit unit markings. For example,
'1 12:59:10'is read the same as
'1 day 12 hours 59 min 10 sec'. Also, a combination of years and months can be specified with a dash; for example
'200-10'is read the same as
'200 years 10 months'. (These shorter forms are in fact the only ones allowed by theSQLstandard, and are used for output when
IntervalStyleis set to
Interval values can also be written as ISO 8601 time intervals, using either the“format with designators”of the standard's section 188.8.131.52 or the“alternative format”of section 184.108.40.206. The format with designators looks like this:
P quantity unit [ quantity unit ... ] [ T [ quantity unit ... ] ]
The string must start with a
P, and may include a
Tthat introduces the time-of-day units. The available unit abbreviations are given inTable 8.16. Units may be omitted, and may be specified in any order, but units smaller than a day must appear after
T. In particular, the meaning of
Mdepends on whether it is before or after
Table 8.16. ISO 8601 Interval Unit Abbreviations
|M||Months (in the date part)|
|M||Minutes (in the time part)|
In the alternative format:
P [ years - months - days ] [ T hours : minutes : seconds ]
the string must begin with
P, and a
Tseparates the date and time parts of the interval. The values are given as numbers similar to ISO 8601 dates.
When writing an interval constant with a
fields_specification, or when assigning a string to an interval column that was defined with a
fieldsspecification, the interpretation of unmarked quantities depends on the
fields. For example
INTERVAL '1' YEARis read as 1 year, whereas
INTERVAL '1'means 1 second. Also, field values“to the right”of the least significant field allowed by the
fields_specification are silently discarded. For example, writing
INTERVAL '1 day 2:03:04' HOUR TO MINUTEresults in dropping the seconds field, but not the day field.
According to theSQLstandard all fields of an interval value must have the same sign, so a leading negative sign applies to all fields; for example the negative sign in the interval literal
'-1 2:03:04'applies to both the days and hour/minute/second parts.PostgreSQLallows the fields to have different signs, and traditionally treats each field in the textual representation as independently signed, so that the hour/minute/second part is considered positive in this example. If
IntervalStyleis set to
sql_standardthen a leading sign is considered to apply to all fields (but only if no additional signs appear). Otherwise the traditionalPostgreSQLinterpretation is used. To avoid ambiguity, it's recommended to attach an explicit sign to each field if any field is negative.
intervalvalues are stored as months, days, and seconds. This is done because the number of days in a month varies, and a day can have 23 or 25 hours if a daylight savings time adjustment is involved. The months and days fields are integers while the seconds field can store fractions. Because intervals are usually created from constant strings or
timestampsubtraction, this storage method works well in most cases. Functions
justify_hoursare available for adjusting days and hours that overflow their normal ranges.
In the verbose input format, and in some fields of the more compact input formats, field values can have fractional parts; for example
'01:02:03.45'. Such input is converted to the appropriate number of months, days, and seconds for storage. When this would result in a fractional number of months or days, the fraction is added to the lower-order fields using the conversion factors 1 month = 30 days and 1 day = 24 hours. For example,
'1.5 month'becomes 1 month and 15 days. Only seconds will ever be shown as fractional on output.
Table 8.17shows some examples of valid
Table 8.17. Interval Input
|1-2||SQL standard format: 1 year 2 months|
|3 4:05:06||SQL standard format: 3 days 4 hours 5 minutes 6 seconds|
|1 year 2 months 3 days 4 hours 5 minutes 6 seconds||Traditional Postgres format: 1 year 2 months 3 days 4 hours 5 minutes 6 seconds|
|P1Y2M3DT4H5M6S||ISO 8601“format with designators”: same meaning as above|
|P0001-02-03T04:05:06||ISO 8601“alternative format”: same meaning as above|
8.5.5. Interval Output
The output format of the interval type can be set to one of the four styles
iso_8601, using the command
SET intervalstyle. The default is the
postgresformat.Table 8.18shows examples of each output style.
sql_standardstyle produces output that conforms to the SQL standard's specification for interval literal strings, if the interval value meets the standard's restrictions (either year-month only or day-time only, with no mixing of positive and negative components). Otherwise the output looks like a standard year-month literal string followed by a day-time literal string, with explicit signs added to disambiguate mixed-sign intervals.
The output of the
postgresstyle matches the output ofPostgreSQLreleases prior to 8.4 when theDateStyleparameter was set to
The output of the
postgres_verbosestyle matches the output ofPostgreSQLreleases prior to 8.4 when the
DateStyleparameter was set to non-
The output of the
iso_8601style matches the“format with designators”described in section 220.127.116.11 of the ISO 8601 standard.
Table 8.18. Interval Output Style Examples
|Style Specification||Year-Month Interval||Day-Time Interval||Mixed Interval|
||1-2||3 4:05:06||-1-2 +3 -4:05:06|
||1 year 2 mons||3 days 04:05:06||-1 year -2 mons +3 days -04:05:06|
||@ 1 year 2 mons||@ 3 days 4 hours 5 mins 6 secs||@ 1 year 2 mons -3 days 4 hours 5 mins 6 secs ago|