Date and Time Processing Functions and Operators

Date and Time Operators

When the user uses date/time operators, explicit type prefixes are modified for corresponding operands to ensure that the operands parsed by the database are consistent with what the user expects, and no unexpected results occur.

For example, abnormal mistakes will occur in the following example without an explicit data type.

1	SELECT date '2001-10-01' - '7' AS RESULT;

Time/Date functions

• age(timestamp, timestamp)

  Description: Subtracts arguments, producing a result in YYYY-MM-DD format. If the result is negative, the returned result is also negative.

  Return type: interval

  For example:

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  SELECT age(timestamp '2001-04-10', timestamp '1957-06-13'); age ------------------------- 43 years 9 mons 27 days (1 row)

• age(timestamp)

  Description: Subtracts from current_date

  Return type: interval

  For example:

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  SELECT age(timestamp '1957-06-13'); age ------------------------- 60 years 2 mons 18 days (1 row)

• timestampdiff(field, timestamp1, timestamp2)

  Description: Subtracts timestamp1 from timestamp2 and returns the difference in the unit of field. If the difference is negative, this function returns it normally. The field can be day, month, quarter, day, week, hour, minute, second, or microsecond.

  Return type: bigint

  For example:

  SELECT timestampdiff(day, timestamp '2001-02-01', timestamp '2003-05-01 12:05:55');
   timestampdiff 
  ---------------
        819
  (1 row)

• clock_timestamp()

  Description: Specifies the current timestamp of the real-time clock.

  Return type: timestamp with time zone

  For example:

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  SELECT clock_timestamp(); clock_timestamp ------------------------------- 2017-09-01 16:57:36.636205+08 (1 row)

• current_date

  Description: Current date

  Return type: date

  For example:

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  SELECT current_date; date ------------ 2017-09-01 (1 row)

• current_time

  Description: Current time

  Return type: time with time zone

  For example:

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  SELECT current_time; timetz -------------------- 16:58:07.086215+08 (1 row)

• current_timestamp

  Description: Specifies the current date and time.

  Return type: timestamp with time zone

  For example:

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  SELECT current_timestamp; pg_systimestamp ------------------------------ 2017-09-01 16:58:19.22173+08 (1 row)

• date_part(text, timestamp)

  Description:

  Description: Obtains the hour.

  Equivalent to extract(field from timestamp).

  Return type: double precision

  For example:

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  SELECT date_part('hour', timestamp '2001-02-16 20:38:40'); date_part ----------- 20 (1 row)

• date_part(text, interval)

  Description:

  Obtains the month. If the value is greater than 12, obtain the remainder after it is divided by 12.

  Equivalent to extract(field from timestamp).

  Return type: double precision

  For example:

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  SELECT date_part('month', interval '2 years 3 months'); date_part ----------- 3 (1 row)

• date_trunc(text, timestamp)

  Description: Truncates to the precision specified by text.

  Return type: timestamp

  For example:

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  SELECT date_trunc('hour', timestamp '2001-02-16 20:38:40'); date_trunc --------------------- 2001-02-16 20:00:00 (1 row)

• trunc(timestamp)

  Description: By default, the data is intercepted by day.

  For example:

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  SELECT trunc(timestamp '2001-02-16 20:38:40'); trunc --------------------- 2001-02-16 00:00:00 (1 row)

• extract(field from timestamp)

  Description: Obtains the hour.

  Return type: double precision

  For example:

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  SELECT extract(hour from timestamp '2001-02-16 20:38:40'); date_part ----------- 20 (1 row)

• extract(field from interval)

  Description: Obtains the month. If the value is greater than 12, obtain the remainder after it is divided by 12.

  Return type: double precision

  For example:

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  SELECT extract(month from interval '2 years 3 months'); date_part ----------- 3 (1 row)

• isfinite(date)

  Description: Tests for valid date.

  Return type: boolean

  For example:

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  SELECT isfinite(date '2001-02-16'); isfinite ---------- t (1 row)

• isfinite(timestamp)

  Description: Tests for valid timestamp.

  Return type: boolean

  For example:

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  SELECT isfinite(timestamp '2001-02-16 21:28:30'); isfinite ---------- t (1 row)

• isfinite(interval)

  Description: Tests for valid interval.

  Return type: boolean

  For example:

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  SELECT isfinite(interval '4 hours'); isfinite ---------- t (1 row)

• justify_days(interval)

  Description: Adjusts interval to 30-day time periods are represented as months

  Return type: interval

  For example:

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  SELECT justify_days(interval '35 days'); justify_days -------------- 1 mon 5 days (1 row)

• justify_hours(interval)

  Description: Adjusts interval to 24-hour time periods are represented as days

  Return type: interval

  For example:

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  SELECT JUSTIFY_HOURS(INTERVAL '27 HOURS'); justify_hours ---------------- 1 day 03:00:00 (1 row)

• justify_interval(interval)

  Description: Adjusts interval using justify_days and justify_hours.

  Return type: interval

  For example:

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  SELECT JUSTIFY_INTERVAL(INTERVAL '1 MON -1 HOUR'); justify_interval ------------------ 29 days 23:00:00 (1 row)

• localtime

  Description: Current time

  Return type: time

  For example:

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  SELECT localtime AS RESULT; result ---------------- 16:05:55.664681 (1 row)

• localtimestamp

  Description: Specifies the current date and time.

  Return type: timestamp

  For example:

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  SELECT localtimestamp; timestamp ---------------------------- 2017-09-01 17:03:30.781902 (1 row)

• now()

  Description: Timestamp indicating the start of the current transaction.

  Return type: timestamp with time zone

  For example:

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  SELECT now(); now ------------------------------- 2017-09-01 17:03:42.549426+08 (1 row)

• numtodsinterval(num, interval_unit)

  Description: Converts a number to the interval type. num is a numeric-typed number. interval_unit is a string in the following format: 'DAY' | 'HOUR' | 'MINUTE' | 'SECOND'

  You can set the IntervalStyle parameter to oracle to be compatible with the interval output format of the function in the Oracle database.

  For example:

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  SELECT numtodsinterval(100, 'HOUR'); numtodsinterval ----------------- 100:00:00 (1 row) SET intervalstyle = oracle; SET SELECT numtodsinterval(100, 'HOUR'); numtodsinterval ------------------------------- +000000004 04:00:00.000000000 (1 row)

• pg_sleep(seconds)

  Description: Specifies the delay time of the server thread in unit of second.

  Return type: void

  For example:

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  SELECT pg_sleep(10); pg_sleep ---------- (1 row)

• statement_timestamp()

  Description: Specifies the current date and time.

  Return type: timestamp with time zone

  For example:

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  SELECT statement_timestamp(); statement_timestamp ------------------------------- 2017-09-01 17:04:39.119267+08 (1 row)

• sysdate

  Description: Specifies the current date and time.

  Return type: timestamp

  For example:

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  SELECT sysdate; sysdate --------------------- 2017-09-01 17:04:49 (1 row)

• timeofday()

  Description: Current date and time (like clock_timestamp, but returned as a text string)

  Return type: text

  For example:

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  SELECT timeofday(); timeofday ------------------------------------- Fri Sep 01 17:05:01.167506 2017 CST (1 row)

• transaction_timestamp()

  Description: Current date and time (equivalent to current_timestamp)

  Return type: timestamp with time zone

  For example:

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  SELECT transaction_timestamp(); transaction_timestamp ------------------------------- 2017-09-01 17:05:13.534454+08 (1 row)

• add_months(d,n)

  Description: Calculates the time point day and time of nth months.

  Return type: timestamp

  For example:

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  SELECT add_months(to_date('2017-5-29', 'yyyy-mm-dd'), 11) FROM dual; add_months --------------------- 2018-04-29 00:00:00 (1 row)

• last_day(d)

  Description: Calculates the time of the last day in the month.

  • In the ORA- or TD-compatible mode, the return type is timestamp.
  • In the MySQL-compatible mode, the return type is date.

  For example:

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  select last_day(to_date('2017-01-01', 'YYYY-MM-DD')) AS cal_result; cal_result --------------------- 2017-01-31 00:00:00 (1 row)

EXTRACT

EXTRACT(field FROM source)

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

• century

  Century

  The first century starts at 0001-01-01 00:00:00 AD. This definition applies to all Gregorian calendar countries. There is no century number 0. You go from -1 century to 1 century.

  For example:

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  SELECT EXTRACT(CENTURY FROM TIMESTAMP '2000-12-16 12:21:13'); date_part ----------- 20 (1 row)

• day
  • For timestamp values, the day (of the month) column (1–31)

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    SELECT EXTRACT(DAY FROM TIMESTAMP '2001-02-16 20:38:40'); date_part ----------- 16 (1 row)

  • For interval values, the number of days

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    SELECT EXTRACT(DAY FROM INTERVAL '40 days 1 minute'); date_part ----------- 40 (1 row)

• decade

  Year column divided by 10

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  SELECT EXTRACT(DECADE FROM TIMESTAMP '2001-02-16 20:38:40'); date_part ----------- 200 (1 row)

• dow

  Day of the week as Sunday(0) to Saturday (6)

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  SELECT EXTRACT(DOW FROM TIMESTAMP '2001-02-16 20:38:40'); date_part ----------- 5 (1 row)

• doy

  Day of the year (1–365 or 366)

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  SELECT EXTRACT(DOY FROM TIMESTAMP '2001-02-16 20:38:40'); date_part ----------- 47 (1 row)

• epoch
  • For timestamp with time zone values, the number of seconds since 1970-01-01 00:00:00 UTC (can be negative);

    for date and timestamp values, the number of seconds since 1970-01-01 00:00:00 local time;

    for interval values, the total number of seconds in the interval.

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    SELECT EXTRACT(EPOCH FROM TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40.12-08'); date_part -------------- 982384720.12 (1 row)

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    SELECT EXTRACT(EPOCH FROM INTERVAL '5 days 3 hours'); date_part ----------- 442800 (1 row)

  • Way to convert an epoch value back to a timestamp

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    SELECT TIMESTAMP WITH TIME ZONE 'epoch' + 982384720.12 * INTERVAL '1 second' AS RESULT; result --------------------------- 2001-02-17 12:38:40.12+08 (1 row)

• hour

  Hour column (0–23)

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  SELECT EXTRACT(HOUR FROM TIMESTAMP '2001-02-16 20:38:40'); date_part ----------- 20 (1 row)

• isodow

  Day of the week (1–7)

  Monday is 1 and Sunday is 7.

  

  This is identical to dow except for Sunday.

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  SELECT EXTRACT(ISODOW FROM TIMESTAMP '2001-02-18 20:38:40'); date_part ----------- 7 (1 row)

• isoyear

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

  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 column for more information.

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  SELECT EXTRACT(ISOYEAR FROM DATE '2006-01-01'); date_part ----------- 2005 (1 row)

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  SELECT EXTRACT(ISOYEAR FROM DATE '2006-01-02'); date_part ----------- 2006 (1 row)

• microseconds

  The seconds column, including fractional parts, multiplied by 1,000,000

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  SELECT EXTRACT(MICROSECONDS FROM TIME '17:12:28.5'); date_part ----------- 28500000 (1 row)

• millennium

  Millennium

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

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  SELECT EXTRACT(MILLENNIUM FROM TIMESTAMP '2001-02-16 20:38:40'); date_part ----------- 3 (1 row)

• milliseconds

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

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  SELECT EXTRACT(MILLISECONDS FROM TIME '17:12:28.5'); date_part ----------- 28500 (1 row)

• minute

  Minutes column (0–59)

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  SELECT EXTRACT(MINUTE FROM TIMESTAMP '2001-02-16 20:38:40'); date_part ----------- 38 (1 row)

• month

  For timestamp values, the number of the month within the year (1–12);

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  SELECT EXTRACT(MONTH FROM TIMESTAMP '2001-02-16 20:38:40'); date_part ----------- 2 (1 row)

  For interval values, the number of months, modulo 12 (0–11)

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  SELECT EXTRACT(MONTH FROM INTERVAL '2 years 13 months'); date_part ----------- 1 (1 row)

• quarter

  Quarter of the year (1–4) that the date is in

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

• second

  Seconds column, including fractional parts (0–59)

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  SELECT EXTRACT(SECOND FROM TIME '17:12:28.5'); date_part ----------- 28.5 (1 row)

• 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, and late December dates to be part of the 1st week of the next year. For example, 2005-01-01 is part of the 53rd week of year 2004, 2006-01-01 is part of the 52nd week of year 2005, and 2012-12-31 is part of the 1st week of year 2013. You are advised to use the columns isoyear and week together to ensure consistency.

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  SELECT EXTRACT(WEEK FROM TIMESTAMP '2001-02-16 20:38:40'); date_part ----------- 7 (1 row)

• year

  Year column

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  SELECT EXTRACT(YEAR FROM TIMESTAMP '2001-02-16 20:38:40'); date_part ----------- 2001 (1 row)

date_part

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

date_part('field', source)

Note that the field must be a string, rather than a name. The valid field names are the same as those for extract. For details, see EXTRACT.

For example:

1
2
3
4
5

SELECT date_part('day', TIMESTAMP '2001-02-16 20:38:40');
 date_part 
-----------
        16
(1 row)

1
2
3
4
5

SELECT date_part('hour', INTERVAL '4 hours 3 minutes');
 date_part 
-----------
         4
(1 row)

date_format

date_format(timestamp, fmt)

Converts a date into a string in the format specified by fmt.

For example:

SELECT date_format('2009-10-04 22:23:00', '%M %D %W');
    date_format
--------------------
 October 4th Sunday
(1 row)
SELECT date_format('2021-02-20 08:30:45', '%Y-%m-%d %H:%i:%S');
     date_format
---------------------
 2021-02-20 08:30:45
(1 row)
SELECT date_format('2021-02-20 18:10:15', '%r-%T');
     date_format
----------------------
 06:10:15 PM-18:10:15
(1 row)

The following table describes the patterns of date parameter values. They can be used for the date_format, time_format, str_to_date, str_to_time, and from_unixtime functions.

In the preceding table, %U, %u, %V, %v, %X, and %x are not supported currently.