Date and Time Processing Functions and Operators
Date and Time Operators
WARNING: 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.
SELECT date '2001-10-01' - '7' AS RESULT;
Table 1 Time and date operators
Time/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:
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:
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.
Return type: timestamp with time zone
Example:
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:
openGauss=# SELECT current_date; date ------------ 2017-09-01 (1 row)current_time
Description: Specifies the current time.
Return type: time with time zone
Example:
openGauss=# 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
Example:
openGauss=# SELECT current_timestamp; pg_systimestamp ------------------------------ 2017-09-01 16:58:19.22173+08 (1 row)date_part(text, timestamp)
Description: Obtains the value of a subdomain in date or time, for example, the year or hour. 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:
openGauss=# SELECT date_part('hour', timestamp '2001-02-16 20:38:40'); date_part ----------- 20 (1 row)date_part(text, interval)
Description: Obtains the subdomain value of the date/time value. When obtaining the month value, 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:
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:
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:
openGauss=# SELECT trunc(timestamp '2001-02-16 20:38:40'); trunc --------------------- 2001-02-16 00:00:00 (1 row)daterange(arg1, arg2)
Description: Obtains time boundary information. The type of arg1 and arg2 is date.
Return type: daterange
Example:
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. The type of arg1 and arg2 is date, and the type of text is text.
Return type: daterange
Example:
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:
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:
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:
openGauss=# SELECT isfinite(date '2001-02-16'); isfinite ---------- t (1 row)isfinite(timestamp)
Description: Tests for a valid timestamp.
Return type: Boolean
Example:
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:
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:
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:
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:
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:
openGauss=# SELECT localtime AS RESULT; result ---------------- 16:05:55.664681 (1 row)localtimestamp
Description: Specifies the current date and time.
Return type: timestamp
Example:
openGauss=# SELECT localtimestamp; timestamp ---------------------------- 2017-09-01 17:03:30.781902 (1 row)now()
Description: Specifies the current date and time.
Return type: timestamp with time zone
Example:
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:
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 a to be compatible with the interval output format of the function.
Example:
openGauss=# SELECT numtodsinterval(100, 'HOUR'); numtodsinterval ----------------- 100:00:00 (1 row) openGauss=# SET intervalstyle = a; 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.
Return type: void
Example:
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:
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:
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:
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:
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.
Return type: timestamp
Example:
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:
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)new_time(date, timezone1,timezone2)
Description: Returns the date and time in timezone2 when date and time in timezone1 are date
Parameter Type: timestamp without time zone, text, text
Return type: timestamp without time zone
Example:
openGauss=# select new_time('2024-07-22 14:00:00', 'EST', 'PST'); new_time --------------------- 2024-07-22 11:00:00 (1 row)
NOTE:1.This function is valid only when openGauss is compatible with dbcompatibility = 'A'.
2.The first parameter date can not be timestamp with time zone.
next_day(x,y)
Description: Calculates the time of the next week y started from x.
Return type: timestamp
Example:
openGauss=# select next_day(timestamp '2017-05-25 00:00:00','Sunday')AS cal_result; cal_result --------------------- 2017-05-28 00:00:00 (1 row)tinterval(abstime, abstime )
Description: Creates a time interval with two pieces of absolute time.
Return type: tinterval
Example:
openGauss=# call tinterval(abstime 'May 10, 1947 23:59:12', abstime 'Mon May 1 00:30:30 1995'); tinterval ----------------------------------------------------- ["1947-05-10 23:59:12+09" "1995-05-01 00:30:30+08"] (1 row)tintervalend(tinterval)
Description: Returns the end time of tinterval.
Return type: abstime
Example:
openGauss=# select tintervalend('["Sep 4, 1983 23:59:12" "Oct4, 1983 23:59:12"]'); tintervalend ------------------------ 1983-10-04 23:59:12+08 (1 row)tintervalrel(tinterval)
Description: Calculates and returns the relative time of tinterval.
Return type: reltime
Example:
openGauss=# select tintervalrel('["Sep 4, 1983 23:59:12" "Oct4, 1983 23:59:12"]'); tintervalrel -------------- 1 mon (1 row)smalldatetime_ge
Description: Checks whether the value of the first parameter is greater than or equal to that of the second parameter.
Parameter: smalldatetime, smalldatetime
Return type: Boolean
smalldatetime_cmp
Description: Compares two smalldatetime values to check whether they are the same.
Parameter: smalldatetime, smalldatetime
Return type: integer
smalldatetime_eq
Description: Compares two smalldatetime values to check whether they are the same.
Parameter: smalldatetime, smalldatetime
Return type: Boolean
smalldatetime_gt
Description: Determines whether the first parameter is greater than the second.
Parameter: smalldatetime, smalldatetime
Return type: Boolean
smalldatetime_hash
Description: Calculates the hash value corresponding to a timestamp.
Parameter: smalldatetime
Return type: integer
smalldatetime_in
Description: Inputs a timestamp.
Parameter: cstring, oid, integer
Return type: smalldatetime
smalldatetime_larger
Description: Returns a larger timestamp.
Parameter: smalldatetime, smalldatetime
Return type: smalldatetime
smalldatetime_le
Description: Checks whether the value of the first parameter is less than or equal to that of the second parameter.
Parameter: smalldatetime, smalldatetime
Return type: Boolean
smalldatetime_lt
Description: Determines whether the first parameter is less than the second parameter.
Parameter: smalldatetime, smalldatetime
Return type: Boolean
smalldatetime_ne
Description: Compares two timestamps to check whether they are different.
Parameter: smalldatetime, smalldatetime
Return type: Boolean
smalldatetime_out
Description: Converts a timestamp into the external form.
Parameter: smalldatetime
Return type: cstring
smalldatetime_send
Description: Converts a timestamp to the binary format.
Parameter: smalldatetime
Return type: bytea
smalldatetime_smaller
Description: Returns a smaller smalldatetime.
Parameter: smalldatetime, smalldatetime
Return type: smalldatetime
smalldatetime_to_abstime
Description: Converts smalldatetime to abstime.
Parameter: smalldatetime
Return type: abstime
smalldatetime_to_time
Description: Converts smalldatetime to time.
Parameter: smalldatetime
Return type: time without time zone
smalldatetime_to_timestamp
Description: Converts smalldatetime to timestamp.
Parameter: smalldatetime
Return type: timestamp without time zone
smalldatetime_to_timestamptz
Description: Converts smalldatetime to timestamptz.
Parameter: smalldatetime
Return type: timestamp with time zone
smalldatetime_to_varchar2
Description: Converts smalldatetime to varchar2.
Parameter: smalldatetime
Return type: character varying
NOTE:
There are multiple methods for obtaining the current time. Select an appropriate API based on the actual service scenario.- The following APIs return values based on the start time of the current transaction:
CURRENT_DATE CURRENT_TIME CURRENT_TIME(precision) CURRENT_TIMESTAMP(precision) LOCALTIME LOCALTIMESTAMP LOCALTIME(precision) LOCALTIMESTAMP(precision)CURRENT_TIME and CURRENT_TIMESTAMP(precision) transfer values with time zones. The values of LOCALTIME and LOCALTIMESTAMP do not contain time zone information. CURRENT_TIME, LOCALTIME, and LOCALTIMESTAMP can be optionally attached with a precision parameter, which rounds the second field of the result to the specified decimal place. If there is no precision parameter, the result is given the full precision that can be obtained. Because these functions all return results by the start time of the current transaction, their values do not change throughout the transaction. We think this is a feature with the purpose to allow a transaction to have a consistent concept at the “current” time, so that multiple modifications in the same transaction can maintain the same timestamp.
- The following APIs return the start time of the current statement:
transaction_timestamp() statement_timestamp() now()transaction_timestamp() is equivalent to CURRENT_TIMESTAMP(precision), and its name clearly reflects its return value. statement_timestamp() returns the start time of the current statement (more accurately, the time when the last instruction is received from the client). The return values of statement_timestamp() and transaction_timestamp() are the same during the execution of the first instruction of a transaction, but may be different in subsequent instructions. now() is equivalent to transaction_timestamp().
- The following APIs return the actual current time when the function is called:
clock_timestamp() returns the actual “current” time, and its value changes even in the same SQL instruction. Similar to clock_timestamp(), timeofday() also returns the actual current time. However, the result of timeofday() is a formatted text string instead of a timestamp with time zone information.clock_timestamp() timeofday()
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 determines the unit of the difference between two dates.
year
Year.
openGauss=# SELECT TIMESTAMPDIFF(YEAR, '2018-01-01', '2020-01-01'); timestamp_diff ---------------- 2 (1 row)quarter
Quarter.
openGauss=# SELECT TIMESTAMPDIFF(QUARTER, '2018-01-01', '2020-01-01'); timestamp_diff ---------------- 8 (1 row)month
Month.
openGauss=# SELECT TIMESTAMPDIFF(MONTH, '2018-01-01', '2020-01-01'); timestamp_diff ---------------- 24 (1 row)week
Week.
openGauss=# SELECT TIMESTAMPDIFF(WEEK, '2018-01-01', '2020-01-01'); timestamp_diff ---------------- 104 (1 row)day
Day.
openGauss=# SELECT TIMESTAMPDIFF(DAY, '2018-01-01', '2020-01-01'); timestamp_diff ---------------- 730 (1 row)hour
Hour.
openGauss=# SELECT TIMESTAMPDIFF(HOUR, '2020-01-01 10:10:10', '2020-01-01 11:11:11'); timestamp_diff ---------------- 1 (1 row)minute
Minute.
openGauss=# SELECT TIMESTAMPDIFF(MINUTE, '2020-01-01 10:10:10', '2020-01-01 11:11:11'); timestamp_diff ---------------- 61 (1 row)second
Second.
openGauss=# SELECT TIMESTAMPDIFF(SECOND, '2020-01-01 10:10:10', '2020-01-01 11:11:11'); timestamp_diff ---------------- 3661 (1 row)microseconds
The seconds column, including fractional parts, is multiplied by 1,000,000.
openGauss=# SELECT TIMESTAMPDIFF(MICROSECOND, '2020-01-01 10:10:10.000000', '2020-01-01 10:10:10.111111'); timestamp_diff ---------------- 111111 (1 row)timestamp_expr with the time zone
openGauss=# SELECT TIMESTAMPDIFF(HOUR,'2020-05-01 10:10:10-01','2020-05-01 10:10:10-03'); 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
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:
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)
openGauss=# SELECT EXTRACT(DAY FROM TIMESTAMP '2001-02-16 20:38:40'); date_part ----------- 16 (1 row)For interval values, the number of days
openGauss=# SELECT EXTRACT(DAY FROM INTERVAL '40 days 1 minute'); date_part ----------- 40 (1 row)
decade
Year column divided by 10
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)
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)
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.
openGauss=# SELECT EXTRACT(EPOCH FROM TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40.12-08'); date_part -------------- 982384720.12 (1 row)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
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)
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.
NOTE:
This is identical to dow except for Sunday.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.
openGauss=# SELECT EXTRACT(ISOYEAR FROM DATE '2006-01-01'); date_part ----------- 2005 (1 row)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.
openGauss=# SELECT EXTRACT(MICROSECONDS FROM TIME '17:12:28.5'); date_part ----------- 28500000 (1 row)millennium
Years in the 1900s are in the second millennium. The third millennium started from January 1, 2001.
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.
openGauss=# SELECT EXTRACT(MILLISECONDS FROM TIME '17:12:28.5'); date_part ----------- 28500 (1 row)minute
Minutes column (0–59).
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).
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).
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.
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).
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.
openGauss=# SELECT EXTRACT(WEEK FROM TIMESTAMP '2001-02-16 20:38:40'); date_part ----------- 7 (1 row)year
Year column.
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:
openGauss=# SELECT date_part('day', TIMESTAMP '2001-02-16 20:38:40');
date_part
-----------
16
(1 row)
openGauss=# SELECT date_part('hour', INTERVAL '4 hours 3 minutes');
date_part
-----------
4
(1 row)
Table 3 specifies the schema for formatting date and time values.
Table 3 Schema for formatting date and time
- If the range of the input two-digit year is between 00 and 49: If the last two digits of the current year are between 00 and 49, the first two digits of the returned year are the same as the first two digits of the current year. If the last two digits of the current year are between 50 and 99, the first two digits of the returned year equal to the first two digits of the current year plus 1.
- If the range of the input two-digit year is between 50 and 99: If the last two digits of the current year are between 00 and 49, the first two digits of the returned year equal to the first two digits of the current year minus 1. If the last two digits of the current year are between 50 and 99, the first two digits of the returned year are the same as the first two digits of the current year.