Date/Time 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.
SELECT date '2001-10-01' - '7' AS RESULT;
Table 1 Time and date operators
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 a time zone 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 a time zone 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 subcolumn in the date or time value, for example, the year or hour. It is equivalent to extract(field from timestamp).
Timestamp type: 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 value of a subcolumn in the date or 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)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'
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)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)
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 timestamp, timestamptz, or** date** type. unit determines the unit of the difference between two dates.
NOTE: This function is valid only when openGauss is compatible with the MY type (that is, dbcompatibility = 'B').
year
Calculates the number of years between two dates.
openGauss=# SELECT TIMESTAMPDIFF(YEAR, '2018-01-01', '2020-01-01'); timestamp_diff ---------------- 2 (1 row)quarter
Calculates the number of quarters between two dates.
openGauss=# SELECT TIMESTAMPDIFF(QUARTER, '2018-01-01', '2020-01-01'); timestamp_diff ---------------- 8 (1 row)month
Calculates the number of months between two dates.
openGauss=# SELECT TIMESTAMPDIFF(MONTH, '2018-01-01', '2020-01-01'); timestamp_diff ---------------- 24 (1 row)week
Calculates the number of weeks between two dates.
openGauss=# SELECT TIMESTAMPDIFF(WEEK, '2018-01-01', '2020-01-01'); timestamp_diff ---------------- 104 (1 row)day
Calculates the number of days between two dates.
openGauss=# SELECT TIMESTAMPDIFF(DAY, '2018-01-01', '2020-01-01'); timestamp_diff ---------------- 730 (1 row)hour
Calculates the number of hours between two pieces of time.
openGauss=# SELECT TIMESTAMPDIFF(HOUR, '2020-01-01 10:10:10', '2020-01-01 11:11:11'); timestamp_diff ---------------- 1 (1 row)minute
Calculates the number of minutes between two pieces of time.
openGauss=# SELECT TIMESTAMPDIFF(MINUTE, '2020-01-01 10:10:10', '2020-01-01 11:11:11'); timestamp_diff ---------------- 61 (1 row)second
Calculates the number of seconds between two pieces of time.
openGauss=# SELECT TIMESTAMPDIFF(SECOND, '2020-01-01 10:10:10', '2020-01-01 11:11:11'); timestamp_diff ---------------- 3661 (1 row)microseconds
Calculates the number of seconds between two pieces of time, including fractional parts, 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 a 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 or time values. source must be a value expression of timestamp, time, or interval type. (Expressions of the date type are cast to timestamp and can therefore be used as well.) field is an identifier or string that specifies the columns to be extracted from the source value. The extract function returns values of double precision type. The following are valid names of field:
century
Specifies the number of centuries.
The first century starts at 0001-01-01 00:00:00 AD. This definition applies to all Gregorian calendar countries. There is no century numbered 0. You go from the 1st century BC to the 1st century AD.
Example:
openGauss=# SELECT EXTRACT(CENTURY FROM TIMESTAMP '2000-12-16 12:21:13'); date_part ----------- 20 (1 row)day
Specifies the date (1–31) of the month for timestamp.
openGauss=# SELECT EXTRACT(DAY FROM TIMESTAMP '2001-02-16 20:38:40'); date_part ----------- 16 (1 row)Specifies the number of days for interval.
openGauss=# SELECT EXTRACT(DAY FROM INTERVAL '40 days 1 minute'); date_part ----------- 40 (1 row)
decade
Specifies the number of decades.
openGauss=# SELECT EXTRACT(DECADE FROM TIMESTAMP '2001-02-16 20:38:40'); date_part ----------- 200 (1 row)dow
Specifies the day of the week. The value range from 0 (indicating Sunday) to 6 (indicating Saturday).
openGauss=# SELECT EXTRACT(DOW FROM TIMESTAMP '2001-02-16 20:38:40'); date_part ----------- 5 (1 row)doy
Specifies the day of the year (1–365 or 1–366).
openGauss=# SELECT EXTRACT(DOY FROM TIMESTAMP '2001-02-16 20:38:40'); date_part ----------- 47 (1 row)epoch
For timestamp with time zone, it specifies the number of seconds since 1970-01-01 00:00:00-00 UTC (can be negative).
For date and timestamp, it specifies the number of seconds since 1970-01-01 00:00:00-00 (local time).
For interval, it specifies 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)The following converts 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
Specifies the hour column (0–23).
openGauss=# SELECT EXTRACT(HOUR FROM TIMESTAMP '2001-02-16 20:38:40'); date_part ----------- 20 (1 row)isodow
Specifies the day of the week (1–7).
1 indicates Monday and 7 indicates Sunday.
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
Specifies the second column, including fractional parts, multiplied by 1,000,000.
openGauss=# SELECT EXTRACT(MICROSECONDS FROM TIME '17:12:28.5'); date_part ----------- 28500000 (1 row)millennium
Specifies the number of millenniums.
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
Specifies the second column, including fractional parts, 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
Specifies the minute column (0–59).
openGauss=# SELECT EXTRACT(MINUTE FROM TIMESTAMP '2001-02-16 20:38:40'); date_part ----------- 38 (1 row)month
For timestamp, it specifies the 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, it specifies the number of months and modulo 12 (0–11).
openGauss=# SELECT EXTRACT(MONTH FROM INTERVAL '2 years 13 months'); date_part ----------- 1 (1 row)quarter
Specifies the 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
Specifies the second 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, and negative values correspond to zones west of UTC.
timezone_hour
Hour part of the time zone offset.
timezone_minute
Minute part 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
Specifies the 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 those 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 2 specifies the schema for formatting date and time values.
Table 2 Schema for formatting date and time values
In the table, the rules for RR to calculate years are as follows:
- 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 are 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 are 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.