Date and Time Processing Functions and Operators

Date and Time Operators

When the user uses date and 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 and Date Functions

• age(timestamp, timestamp)

  Description: Subtracts parameters, producing a result in YYYY-MM-DD format. If the result is negative, the returned result is also negative. The input parameters can contain timezone or not.

  Return type: interval

  Example:

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

• age(timestamp)

  Description: Minuses the current time with the parameter. The input parameter can contain timezone or not.

  Return type: interval

  Example:

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

• clock_timestamp()

  Description: Specifies the current timestamp of the real-time clock. The volatile function obtains the latest timestamp for each scan. Therefore, the result of each call in a query is different.

  Return type: timestamp with time zone

  Example:

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

• current_date

  Description: Specifies the current date.

  Return type: date

  Example:

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

• current_time

  Description: Specifies the current time.

  Return type: time with time zone

  Example:

  1 2 3 4 5

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

• current_timestamp

  Description: Specifies the current date and time. This is a statement-level timestamp. The returned results within the same statement remain unchanged.

  Return type: timestamp with time zone

  Example:

  1 2 3 4 5

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

• date_part(text, timestamp)

  Description:

  Retrieves subcolumns such as year or hour from date/time values.

  It is equivalent to extract(field from timestamp).

  Timestamp types: abstime, date, interval, reltime, time with time zone, time without time zone, timestamp with time zone, timestamp without time zone

  Return type: double precision

  Example:

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  openGauss=# 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. It is equivalent to extract(field from timestamp).

  Return type: double precision

  Example:

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  openGauss=# 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: interval, timestamp with time zone, timestamp without time zone

  Example:

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

• trunc(timestamp)

  Description: Truncates to day by default.

  Example:

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

• trunc(arg1, arg2)

  Description: Truncates to the precision specified by arg2.

  Type of arg1: interval, timestamp with time zone, timestamp without time zone

  Type of arg2: text

  Return type: interval, timestamp with time zone, timestamp without time zone

  Example:

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  openGauss=# SELECT trunc(timestamp '2001-02-16 20:38:40', 'hour'); trunc --------------------- 2001-02-16 20:00:00 (1 row)

• daterange(arg1, arg2)

  Description: Obtains time boundary information.

  arg1 type: date

  arg2 type: date

  Return type: daterange

  Example:

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  openGauss=# select daterange('2000-05-06','2000-08-08'); daterange ------------------------- [2000-05-06,2000-08-08) (1 row)

• daterange(arg1, arg2, text)

  Description: Obtains time boundary information.

  arg1 type: date

  arg2 type: date

  text type: text

  Return type: daterange

  Example:

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  openGauss=# select daterange('2000-05-06','2000-08-08','[]'); daterange ------------------------- [2000-05-06,2000-08-09) (1 row)

• extract(field from timestamp)

  Description: Obtains the hour.

  Return type: double precision

  Example:

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  openGauss=# 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

  Example:

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

• isfinite(date)

  Description: Tests for a valid date.

  Return type: Boolean

  Example:

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

• isfinite(timestamp)

  Description: Tests for a valid timestamp.

  Return type: Boolean

  Example:

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

• isfinite(interval)

  Description: Tests for a valid interval.

  Return type: Boolean

  Example:

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

• justify_days(interval)

  Description: Adjusts intervals to 30-day time periods, which are represented as months.

  Return type: interval

  Example:

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

• justify_hours(interval)

  Description: Sets the time interval in days (24 hours is one day).

  Return type: interval

  Example:

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  openGauss=# 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

  Example:

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

• localtime

  Description: Specifies the current time.

  Return type: time

  Example:

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

• localtimestamp

  Description: Specifies the current date and time.

  Return type: timestamp

  Example:

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

• now()

  Description: Specifies the current date and time. This is a transaction-level timestamp. The results returned within the same transaction remain unchanged.

  Return type: timestamp with time zone

  Example:

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

• timenow()

  Description: Specifies the current date and time.

  Return type: timestamp with time zone

  Example:

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  openGauss=# select timenow(); timenow ------------------------ 2020-06-23 20:36:56+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.

  Example:

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  openGauss=# SELECT numtodsinterval(100, 'HOUR'); numtodsinterval ----------------- 100:00:00 (1 row) openGauss=# SET intervalstyle = oracle; SET openGauss=# 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. Note that when the database invokes this function, the corresponding transaction snapshot is obtained, which is equivalent to a long transaction. If the input parameter time is too long, the database oldestxmin may fail to be executed, affecting the table recycling and query performance.

  Return type: void

  Example:

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  openGauss=# SELECT pg_sleep(10); pg_sleep ---------- (1 row)

• statement_timestamp()

  Description: Specifies the current date and time.

  Return type: timestamp with time zone

  Example:

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  openGauss=# 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

  Example:

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

• timeofday()

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

  Return type: text

  Example:

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

• transaction_timestamp()

  Description: Specifies the current date and time (equivalent to current_timestamp)

  Return type: timestamp with time zone

  Example:

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

• add_months(d,n)

  Description: Returns the date date plus integer months.

  d: indicates the value of the timestamp type and the value that can be implicitly converted to the timestamp type.

  n: indicates the value of the INTEGER type and the value that can be implicitly converted to the INTEGER type.

  Return type: timestamp

  Example:

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

• last_day(d)

  Description: Returns the date of the last day of the month that contains date.

  Return type: timestamp

  Example:

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

TIMESTAMPDIFF

• TIMESTAMPDIFF(unit , timestamp_expr1, timestamp_expr2)

  The timestampdiff function returns the result of timestamp_expr2 - timestamp_expr1 in the specified unit. timestamp_expr1 and timestamp_expr2 must be value expressions of the timestamp, timestamptz, or date type. unit specifies the unit of the difference between two dates.

  

  This function is valid only when GaussDB is compatible with MySQL (that is, dbcompatibility is set to 'MYSQL').

• year

  Year.

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  openGauss=# SELECT TIMESTAMPDIFF(YEAR, '2018-01-01', '2020-01-01'); timestamp_diff ---------------- 2 (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.

  Example:

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

• decade

  Year column divided by 10

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  openGauss=# 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)

  1 2 3 4 5

  openGauss=# 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)

  1 2 3 4 5

  openGauss=# 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 00:00:00-00 UTC (can be negative).

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

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

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

    1 2 3 4 5

    openGauss=# 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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    openGauss=# 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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  openGauss=# 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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  openGauss=# 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 January 4, so in early January or late December the ISO year may be different from the Gregorian year. See the week column for more information.

  1 2 3 4 5

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

  1 2 3 4 5

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

• microseconds

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

  1 2 3 4 5

  openGauss=# 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.

  1 2 3 4 5

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

• milliseconds

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

  1 2 3 4 5

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

• minute

  Minutes column (0–59).

  1 2 3 4 5

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

• month

  For timestamp values, the specific month in the year (1–12).

  1 2 3 4 5

  openGauss=# 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).

  1 2 3 4 5

  openGauss=# 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.

  1 2 3 4 5

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

• second

  Seconds column, including fractional parts (0–59).

  1 2 3 4 5

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

• timezone

  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

  Hour component of the time zone offset.

• timezone_minute

  Minute component of the time zone offset.

• week

  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.

  1 2 3 4 5

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

• year

  Year column.

  1 2 3 4 5

  openGauss=# 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 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. For details, see EXTRACT.

Example:

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

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