PostgreSQL日期函數備忘

http://www.postgresql.org/docs/current/static/functions-formatting.html

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Date/Time Functions and Operators

Table 9-27?shows the available functions for date/time value processing, with details appearing in the following subsections.?Table 9-26?illustrates the behaviors of the basic arithmetic operators (+,?*, etc.). For formatting functions, refer to?Section 9.8. You should be familiar with the background information on date/time data types from?Section 8.5.

All the functions and operators described below that take?time?or?timestamp?inputs actually come in two variants: one that takes?time with time zone?ortimestamp with time zone, and one that takes?time without time zone?or?timestamp without time zone. For brevity, these variants are not shown separately. Also, the?+?and?*?operators come in commutative pairs (for example both date + integer and integer + date); we show only one of each such pair.

Table 9-26. Date/Time Operators

OperatorExampleResult

+	date '2001-09-28' + integer '7'	date '2001-10-05'
+	date '2001-09-28' + interval '1 hour'	timestamp '2001-09-28 01:00:00'
+	date '2001-09-28' + time '03:00'	timestamp '2001-09-28 03:00:00'
+	interval '1 day' + interval '1 hour'	interval '1 day 01:00:00'
+	timestamp '2001-09-28 01:00' + interval '23 hours'	timestamp '2001-09-29 00:00:00'
+	time '01:00' + interval '3 hours'	time '04:00:00'
-	- interval '23 hours'	interval '-23:00:00'
-	date '2001-10-01' - date '2001-09-28'	integer '3'?(days)
-	date '2001-10-01' - integer '7'	date '2001-09-24'
-	date '2001-09-28' - interval '1 hour'	timestamp '2001-09-27 23:00:00'
-	time '05:00' - time '03:00'	interval '02:00:00'
-	time '05:00' - interval '2 hours'	time '03:00:00'
-	timestamp '2001-09-28 23:00' - interval '23 hours'	timestamp '2001-09-28 00:00:00'
-	interval '1 day' - interval '1 hour'	interval '1 day -01:00:00'
-	timestamp '2001-09-29 03:00' - timestamp '2001-09-27 12:00'	interval '1 day 15:00:00'
*	900 * interval '1 second'	interval '00:15:00'
*	21 * interval '1 day'	interval '21 days'
*	double precision '3.5' * interval '1 hour'	interval '03:30:00'
/	interval '1 hour' / double precision '1.5'	interval '00:40:00'

Table 9-27. Date/Time Functions

FunctionReturn TypeDescriptionExampleResult

age(timestamp,?timestamp)	interval	Subtract arguments, producing a?"symbolic"?result that uses years and months	age(timestamp '2001-04-10', timestamp '1957-06-13')	43 years 9 mons 27 days
age(timestamp)	interval	Subtract from?current_date?(at midnight)	age(timestamp '1957-06-13')	43 years 8 mons 3 days
clock_timestamp()	timestamp with time zone	Current date and time (changes during statement execution); see?Section 9.9.4	?	?
current_date	date	Current date; see?Section 9.9.4	?	?
current_time	time with time zone	Current time of day; see?Section 9.9.4	?	?
current_timestamp	timestamp with time zone	Current date and time (start of current transaction); seeSection 9.9.4	?	?
date_part(text,?timestamp)	double precision	Get subfield (equivalent to?extract); see?Section 9.9.1	date_part('hour', timestamp '2001-02-16 20:38:40')	20
date_part(text,?interval)	double precision	Get subfield (equivalent to?extract); see?Section 9.9.1	date_part('month', interval '2 years 3 months')	3
date_trunc(text,timestamp)	timestamp	Truncate to specified precision; see also?Section 9.9.2	date_trunc('hour', timestamp '2001-02-16 20:38:40')	2001-02-16 20:00:00
extract(field?fromtimestamp)	double precision	Get subfield; see?Section 9.9.1	extract(hour from timestamp '2001-02-16 20:38:40')	20
extract(field?frominterval)	double precision	Get subfield; see?Section 9.9.1	extract(month from interval '2 years 3 months')	3
isfinite(date)	boolean	Test for finite date (not +/-infinity)	isfinite(date '2001-02-16')	true
isfinite(timestamp)	boolean	Test for finite time stamp (not +/-infinity)	isfinite(timestamp '2001-02-16 21:28:30')	true
isfinite(interval)	boolean	Test for finite interval	isfinite(interval '4 hours')	true
justify_days(interval)	interval	Adjust interval so 30-day time periods are represented as months	justify_days(interval '35 days')	1 mon 5 days
justify_hours(interval)	interval	Adjust interval so 24-hour time periods are represented as days	justify_hours(interval '27 hours')	1 day 03:00:00
justify_interval(interval)	interval	Adjust interval using?justify_days?and?justify_hours, with additional sign adjustments	justify_interval(interval '1 mon -1 hour')	29 days 23:00:00
localtime	time	Current time of day; see?Section 9.9.4	?	?
localtimestamp	timestamp	Current date and time (start of current transaction); seeSection 9.9.4	?	?
now()	timestamp with time zone	Current date and time (start of current transaction); seeSection 9.9.4	?	?
statement_timestamp()	timestamp with time zone	Current date and time (start of current statement); seeSection 9.9.4	?	?
timeofday()	text	Current date and time (like?clock_timestamp, but as a?textstring); see?Section 9.9.4	?	?
transaction_timestamp()	timestamp with time zone	Current date and time (start of current transaction); seeSection 9.9.4	?	?

In addition to these functions, the SQL?OVERLAPS?operator is supported:

(start1, end1) OVERLAPS (start2, end2) (start1, length1) OVERLAPS (start2, length2)

This expression yields true when two time periods (defined by their endpoints) overlap, false when they do not overlap. The endpoints can be specified as pairs of dates, times, or time stamps; or as a date, time, or time stamp followed by an interval. When a pair of values is provided, either the start or the end can be written first;?OVERLAPS?automatically takes the earlier value of the pair as the start. Each time period is considered to represent the half-open interval?start?<=?time?<?end, unless?start?and?end?are equal in which case it represents that single time instant. This means for instance that two time periods with only an endpoint in common do not overlap.

SELECT (DATE '2001-02-16', DATE '2001-12-21') OVERLAPS(DATE '2001-10-30', DATE '2002-10-30'); Result: true SELECT (DATE '2001-02-16', INTERVAL '100 days') OVERLAPS(DATE '2001-10-30', DATE '2002-10-30'); Result: false SELECT (DATE '2001-10-29', DATE '2001-10-30') OVERLAPS(DATE '2001-10-30', DATE '2001-10-31'); Result: false SELECT (DATE '2001-10-30', DATE '2001-10-30') OVERLAPS(DATE '2001-10-30', DATE '2001-10-31'); Result: true

When adding an?interval?value to (or subtracting an?interval?value from) a?timestamp with time zone?value, the days component advances (or decrements) the date of the?timestamp with time zone?by the indicated number of days. Across daylight saving time changes (with the session time zone set to a time zone that recognizes DST), this means?interval '1 day'?does not necessarily equal?interval '24 hours'. For example, with the session time zone set to?CST7CDT,?timestamp with time zone '2005-04-02 12:00-07' + interval '1 day'?will produce?timestamp with time zone '2005-04-03 12:00-06', while adding?interval '24 hours'?to the same initial?timestamp with time zone?produces?timestamp with time zone '2005-04-03 13:00-06', as there is a change in daylight saving time at?2005-04-03 02:00?in time zone?CST7CDT.

Note there can be ambiguity in the?months?returned by?age?because different months have a different number of days.?PostgreSQL's approach uses the month from the earlier of the two dates when calculating partial months. For example,?age('2004-06-01', '2004-04-30')?uses April to yield?1 mon 1 day, while using May would yield?1 mon 2 days?because May has 31 days, while April has only 30.

9.9.1.?EXTRACT,?date_part

EXTRACT(field FROM source)

The?extract?function retrieves subfields such as year or hour from date/time values.?source?must be a value expression of type?timestamp,?time, orinterval. (Expressions of type?date?are cast to?timestamp?and can therefore be used as well.)?field?is an identifier or string that selects what field to extract from the source value. The?extract?function returns values of type?double precision. The following are valid field names:

?

?

century

The century

SELECT EXTRACT(CENTURY FROM TIMESTAMP '2000-12-16 12:21:13'); Result: 20 SELECT EXTRACT(CENTURY FROM TIMESTAMP '2001-02-16 20:38:40'); Result: 21

The first century starts at 0001-01-01 00:00:00 AD, although they did not know it at the time. This definition applies to all Gregorian calendar countries. There is no century number 0, you go from -1 century to 1 century. If you disagree with this, please write your complaint to: Pope, Cathedral Saint-Peter of Roma, Vatican.

PostgreSQL?releases before 8.0 did not follow the conventional numbering of centuries, but just returned the year field divided by 100.

day

The day (of the month) field (1 - 31)

SELECT EXTRACT(DAY FROM TIMESTAMP '2001-02-16 20:38:40'); Result: 16

decade

The year field divided by 10

SELECT EXTRACT(DECADE FROM TIMESTAMP '2001-02-16 20:38:40'); Result: 200

dow

The day of the week as Sunday(0) to Saturday(6)

SELECT EXTRACT(DOW FROM TIMESTAMP '2001-02-16 20:38:40'); Result: 5

Note that?extract's day of the week numbering differs from that of the?to_char(..., 'D')?function.

doy

The day of the year (1 - 365/366)

SELECT EXTRACT(DOY FROM TIMESTAMP '2001-02-16 20:38:40'); Result: 47

epoch

For?date?and?timestamp?values, the number of seconds since 1970-01-01 00:00:00 UTC (can be negative); for?interval?values, the total number of seconds in the interval

SELECT EXTRACT(EPOCH FROM TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40.12-08'); Result: 982384720.12SELECT EXTRACT(EPOCH FROM INTERVAL '5 days 3 hours'); Result: 442800

Here is how you can convert an epoch value back to a time stamp:

SELECT TIMESTAMP WITH TIME ZONE 'epoch' + 982384720.12 * INTERVAL '1 second';

(The?to_timestamp?function encapsulates the above conversion.)

hour

The hour field (0 - 23)

SELECT EXTRACT(HOUR FROM TIMESTAMP '2001-02-16 20:38:40'); Result: 20

isodow

The day of the week as Monday(1) to Sunday(7)

SELECT EXTRACT(ISODOW FROM TIMESTAMP '2001-02-18 20:38:40'); Result: 7

This is identical to?dow?except for Sunday. This matches the?ISO?8601 day of the week numbering.

isoyear

The?ISO?8601 year that the date falls in (not applicable to intervals)

SELECT EXTRACT(ISOYEAR FROM DATE '2006-01-01'); Result: 2005 SELECT EXTRACT(ISOYEAR FROM DATE '2006-01-02'); Result: 2006

Each?ISO?year begins with the Monday of the week containing the 4th of January, so in early January or late December the?ISO?year may be different from the Gregorian year. See the?week?field for more information.

This field is not available in PostgreSQL releases prior to 8.3.

microseconds

The seconds field, including fractional parts, multiplied by 1 000 000; note that this includes full seconds

SELECT EXTRACT(MICROSECONDS FROM TIME '17:12:28.5'); Result: 28500000

millennium

The millennium

SELECT EXTRACT(MILLENNIUM FROM TIMESTAMP '2001-02-16 20:38:40'); Result: 3

Years in the 1900s are in the second millennium. The third millennium started January 1, 2001.

PostgreSQL?releases before 8.0 did not follow the conventional numbering of millennia, but just returned the year field divided by 1000.

milliseconds

The seconds field, including fractional parts, multiplied by 1000. Note that this includes full seconds.

SELECT EXTRACT(MILLISECONDS FROM TIME '17:12:28.5'); Result: 28500

minute

The minutes field (0 - 59)

SELECT EXTRACT(MINUTE FROM TIMESTAMP '2001-02-16 20:38:40'); Result: 38

month

For?timestamp?values, the number of the month within the year (1 - 12) ; for?interval?values the number of months, modulo 12 (0 - 11)

SELECT EXTRACT(MONTH FROM TIMESTAMP '2001-02-16 20:38:40'); Result: 2SELECT EXTRACT(MONTH FROM INTERVAL '2 years 3 months'); Result: 3SELECT EXTRACT(MONTH FROM INTERVAL '2 years 13 months'); Result: 1

quarter

The quarter of the year (1 - 4) that the date is in

SELECT EXTRACT(QUARTER FROM TIMESTAMP '2001-02-16 20:38:40'); Result: 1

second

The seconds field, including fractional parts (0 - 59[1])

SELECT EXTRACT(SECOND FROM TIMESTAMP '2001-02-16 20:38:40'); Result: 40SELECT EXTRACT(SECOND FROM TIME '17:12:28.5'); Result: 28.5

timezone

The time zone offset from UTC, measured in seconds. Positive values correspond to time zones east of UTC, negative values to zones west of UTC.

timezone_hour

The hour component of the time zone offset

timezone_minute

The minute component of the time zone offset

week

The number of the week of the year that the day is in. By definition (ISO?8601), the first week of a year contains January 4 of that year. (The?ISO-8601 week starts on Monday.) In other words, the first Thursday of a year is in week 1 of that year.

Because of this, it is possible for early January dates to be part of the 52nd or 53rd week of the previous year. For example,?2005-01-01?is part of the 53rd week of year 2004, and?2006-01-01?is part of the 52nd week of year 2005.

SELECT EXTRACT(WEEK FROM TIMESTAMP '2001-02-16 20:38:40'); Result: 7

year

The year field. Keep in mind there is no?0 AD, so subtracting?BC?years from?AD?years should be done with care.

SELECT EXTRACT(YEAR FROM TIMESTAMP '2001-02-16 20:38:40'); Result: 2001

?

The?extract?function is primarily intended for computational processing. For formatting date/time values for display, see?Section 9.8.

The?date_part?function is modeled on the traditional?Ingres?equivalent to the?SQL-standard function?extract:

date_part('field', source)

Note that here the?field?parameter needs to be a string value, not a name. The valid field names for?date_part?are the same as for?extract.

SELECT date_part('day', TIMESTAMP '2001-02-16 20:38:40'); Result: 16SELECT date_part('hour', INTERVAL '4 hours 3 minutes'); Result: 4

9.9.2.?date_trunc

The function?date_trunc?is conceptually similar to the?trunc?function for numbers.

?

date_trunc('field', source)

source?is a value expression of type?timestamp?or?interval. (Values of type?date?and?time?are cast automatically to?timestamp?or?interval, respectively.)field?selects to which precision to truncate the input value. The return value is of type?timestamp?or?interval?with all fields that are less significant than the selected one set to zero (or one, for day and month).

Valid values for?field?are:

?

microseconds

milliseconds

second

minute

hour

day

week

month

quarter

year

decade

century

millennium

?

?

Examples:

SELECT date_trunc('hour', TIMESTAMP '2001-02-16 20:38:40'); Result: 2001-02-16 20:00:00SELECT date_trunc('year', TIMESTAMP '2001-02-16 20:38:40'); Result: 2001-01-01 00:00:00

?

9.9.3.?AT TIME ZONE

The?AT TIME ZONE?construct allows conversions of time stamps to different time zones.?Table 9-28?shows its variants.

Table 9-28.?AT TIME ZONE?Variants

ExpressionReturn TypeDescription

timestamp without time zone?AT TIME ZONEzone	timestamp with time zone	Treat given time stamp?without time zone?as located in the specified time zone
timestamp with time zone?AT TIME ZONE?zone	timestamp without time zone	Convert given time stamp?with time zone?to the new time zone, with no time zone designation
time with time zone?AT TIME ZONE?zone	time with time zone	Convert given time?with time zone?to the new time zone

In these expressions, the desired time zone?zone?can be specified either as a text string (e.g.,?'PST') or as an interval (e.g.,?INTERVAL '-08:00'). In the text case, a time zone name can be specified in any of the ways described in?Section 8.5.3.

Examples (assuming the local time zone is?PST8PDT):

SELECT TIMESTAMP '2001-02-16 20:38:40' AT TIME ZONE 'MST'; Result: 2001-02-16 19:38:40-08SELECT TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40-05' AT TIME ZONE 'MST'; Result: 2001-02-16 18:38:40

The first example takes a time stamp without time zone and interprets it as MST time (UTC-7), which is then converted to PST (UTC-8) for display. The second example takes a time stamp specified in EST (UTC-5) and converts it to local time in MST (UTC-7).

The function?timezone(zone,?timestamp)?is equivalent to the SQL-conforming construct?timestamp?AT TIME ZONE?zone.

9.9.4. Current Date/Time

PostgreSQL?provides a number of functions that return values related to the current date and time. These SQL-standard functions all return values based on the start time of the current transaction:

CURRENT_DATE CURRENT_TIME CURRENT_TIMESTAMP CURRENT_TIME(precision) CURRENT_TIMESTAMP(precision) LOCALTIME LOCALTIMESTAMP LOCALTIME(precision) LOCALTIMESTAMP(precision)

?

CURRENT_TIME?and?CURRENT_TIMESTAMP?deliver values with time zone;?LOCALTIME?and?LOCALTIMESTAMP?deliver values without time zone.

CURRENT_TIME,?CURRENT_TIMESTAMP,?LOCALTIME, and?LOCALTIMESTAMP?can optionally take a precision parameter, which causes the result to be rounded to that many fractional digits in the seconds field. Without a precision parameter, the result is given to the full available precision.

Some examples:

SELECT CURRENT_TIME; Result: 14:39:53.662522-05SELECT CURRENT_DATE; Result: 2001-12-23SELECT CURRENT_TIMESTAMP; Result: 2001-12-23 14:39:53.662522-05SELECT CURRENT_TIMESTAMP(2); Result: 2001-12-23 14:39:53.66-05SELECT LOCALTIMESTAMP; Result: 2001-12-23 14:39:53.662522

?

Since these functions return the start time of the current transaction, their values do not change during the transaction. This is considered a feature: the intent is to allow a single transaction to have a consistent notion of the?"current"?time, so that multiple modifications within the same transaction bear the same time stamp.

Note:?Other database systems might advance these values more frequently.

PostgreSQL?also provides functions that return the start time of the current statement, as well as the actual current time at the instant the function is called. The complete list of non-SQL-standard time functions is:

transaction_timestamp() statement_timestamp() clock_timestamp() timeofday() now()

?

transaction_timestamp()?is equivalent to?CURRENT_TIMESTAMP, but is named to clearly reflect what it returns.?statement_timestamp()?returns the start time of the current statement (more specifically, the time of receipt of the latest command message from the client).?statement_timestamp()?andtransaction_timestamp()?return the same value during the first command of a transaction, but might differ during subsequent commands.clock_timestamp()?returns the actual current time, and therefore its value changes even within a single SQL command.?timeofday()?is a historicalPostgreSQL?function. Like?clock_timestamp(), it returns the actual current time, but as a formatted?text?string rather than a?timestamp with time zonevalue.?now()?is a traditional?PostgreSQL?equivalent to?transaction_timestamp().

All the date/time data types also accept the special literal value?now?to specify the current date and time (again, interpreted as the transaction start time). Thus, the following three all return the same result:

SELECT CURRENT_TIMESTAMP; SELECT now(); SELECT TIMESTAMP 'now'; -- incorrect for use with DEFAULT

?

Tip:?You do not want to use the third form when specifying a?DEFAULT?clause while creating a table. The system will convert?now?to atimestamp?as soon as the constant is parsed, so that when the default value is needed, the time of the table creation would be used! The first two forms will not be evaluated until the default value is used, because they are function calls. Thus they will give the desired behavior of defaulting to the time of row insertion.

9.9.5. Delaying Execution

The following function is available to delay execution of the server process:

pg_sleep(seconds)

pg_sleep?makes the current session's process sleep until?seconds?seconds have elapsed.?seconds?is a value of type?double precision, so fractional-second delays can be specified. For example:

SELECT pg_sleep(1.5);

轉載于:https://www.cnblogs.com/wangyhua/p/4050519.html

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