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Date and Time Processing Functions and Operators

Date and Time Operators

For details about the time and date operators, see Table 1.

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.

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SELECT date '2001-10-01' - '7' AS RESULT;
Table 1 Time and date operators

Operator

Example

+

 
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gaussdb=# SELECT date '2001-9-28' + integer '7' AS RESULT;
   result
------------
 2001-10-05
(1 row)
NOTE:
  • In A compatibility mode, the query result is 2001-10-05 00:00:00.
  • In B compatibility mode (sql_compatibility is set to 'B', b_format_version is set to '5.7' and b_format_dev_version is set to 's1'), the query result is 2001-10-05.
 
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gaussdb=# SELECT date '2001-09-28' + interval '1 hour' AS RESULT;
       result        
---------------------
 2001-09-28 01:00:00
(1 row)

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gaussdb=# SELECT date '2001-09-28' + time '03:00' AS RESULT;
       result        
---------------------
 2001-09-28 03:00:00
(1 row)

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gaussdb=# SELECT interval '1 day' + interval '1 hour' AS RESULT;
     result     
----------------
 1 day 01:00:00
(1 row)

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gaussdb=# SELECT timestamp '2001-09-28 01:00' + interval '23 hours' AS RESULT;
       result        
---------------------
 2001-09-29 00:00:00
(1 row)

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gaussdb=# SELECT time '01:00' + interval '3 hours' AS RESULT;
  result  
----------
 04:00:00
(1 row)

-

 
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gaussdb=# SELECT date '2001-10-01' - date '2001-09-28' AS RESULT;
 result
--------
 3days
(1 row)

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gaussdb=# SELECT date '2001-10-01' - integer '7' AS RESULT;
       result        
---------------------
 2001-09-24 00:00:00
(1 row)

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gaussdb=# SELECT date '2001-09-28' - interval '1 hour' AS RESULT;
       result        
---------------------
 2001-09-27 23:00:00
(1 row)

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gaussdb=# SELECT time '05:00' - time '03:00' AS RESULT;
  result  
----------
 02:00:00
(1 row)

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gaussdb=# SELECT time '05:00' - interval '2 hours' AS RESULT;
  result  
----------
 03:00:00
(1 row)

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gaussdb=# SELECT timestamp '2001-09-28 23:00' - interval '23 hours' AS RESULT;
       result        
---------------------
 2001-09-28 00:00:00
(1 row)

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gaussdb=# SELECT interval '1 day' - interval '1 hour' AS RESULT;
  result  
----------
 23:00:00
(1 row)

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gaussdb=# SELECT timestamp '2001-09-29 03:00' - timestamp '2001-09-27 12:00' AS RESULT;
     result     
----------------
 1 day 15:00:00
(1 row)

*

 
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gaussdb=# SELECT 900 * interval '1 second' AS RESULT;
  result  
----------
 00:15:00
(1 row)

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gaussdb=# SELECT 21 * interval '1 day' AS RESULT;
 result  
---------
 21 days
(1 row)

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gaussdb=# SELECT double precision '3.5' * interval '1 hour' AS RESULT;
  result  
----------
 03:30:00
(1 row)

/

 
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gaussdb=# SELECT interval '1 hour' / double precision '1.5' AS RESULT;
  result  
----------
 00:40:00
(1 row)

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 time zone or not.

    Return type: interval

    Example:

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

    Description: Subtracts the parameter value from the system time when the current SQL statement starts to be executed. The input parameter may or may not contain a time zone.

    Return type: interval

    Example:

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

    Description: Returns the timestamp of the system time when the current function is called. 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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    gaussdb=# SELECT clock_timestamp();
        clock_timestamp        
-------------------------------
 2017-09-01 16:57:36.636205+08
(1 row)
  • current_date

    Description: Returns the system date when the current SQL statement starts.

    Return type: date

    Example:

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

    When a_format_version is set to 10c and a_format_dev_version is set to s2 in an A-compatible database, the return value type is timestamp.

  • current_time

    Description: Specifies the system time when the current transaction starts.

    Return type: time with time zone

    Example:

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

    Description: Returns the system time when the current SQL execution starts. This is a statement-level timestamp. The returned results within the same statement remain unchanged.

    Return type: timestamp with time zone

    Example:

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

    Description: Returns the system time when the current SQL statement is started, and rounds the microseconds of the result to the specified decimal places.

    Return type: timestamp with time zone

    Example:

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    gaussdb=# SELECT current_timestamp(1);
       timestamptz            
------------------------------
 2017-09-01 16:58:19.2+08
(1 row)
    • When a_format_version is set to 10c and a_format_dev_version is set to s2 in an A-compatible database, the precision parameter can be an integer of the numeric type. Otherwise, only the int type is supported.
    • The last digit 0 of the microsecond field is not displayed. For example, 2017-09-01 10:32:19.212000 is displayed as 2017-09-01 10:32:19.212.
  • pg_systimestamp()

    Description: Current date and time (start of the current statement)

    Return type: timestamp with time zone

    Example:

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    gaussdb=# SELECT pg_systimestamp();
        pg_systimestamp
-------------------------------
 2015-10-14 11:21:28.317367+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:

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    gaussdb=# 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:

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    gaussdb=# 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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    gaussdb=# 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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    gaussdb=# 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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    gaussdb=# SELECT trunc(timestamp  '2001-02-16 20:38:40', 'hour');                                                                                                                                                                   trunc
---------------------
2001-02-16 20:00:00
(1 row)
  • round(arg1, arg2)

    Description: Rounds off to the precision specified by arg2.

    Type of arg1: timestamp without time zone

    Type of arg2: text

    Return type: timestamp without time zone

    Example:

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    gaussdb=# SELECT round(timestamp  '2001-02-16 20:38:40', 'hour');                                                                                                                                                                   round
---------------------
2001-02-16 21:00:00
(1 row)

    This function is valid only when the value of a_format_version is 10c and the value of a_format_dev_version is s1 in an A-compatible database.

  • daterange(arg1, arg2)

    Description: Obtains time boundary information. The type of arg1 and arg2 is date.

    Return type: daterange

    Example:

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    gaussdb=# 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:

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    gaussdb=# 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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    gaussdb=# 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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    gaussdb=# SELECT extract(month from interval '2 years 3 months');
 date_part 
-----------
         3
(1 row)
  • isfinite(date)

    Description: Checks whether a date is a finite value. If yes, t is returned. Otherwise, f is returned.

    Return type: Boolean

    Example:

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    gaussdb=# SELECT isfinite(date '2001-02-16');
 isfinite 
----------
 t
(1 row)
gaussdb=# SELECT isfinite(date 'infinity');
 isfinite 
----------
 f
(1 row)
  • isfinite(timestamp)

    Description: Checks whether a timestamp is a finite value. If yes, t is returned. Otherwise, f is returned.

    Return type: Boolean

    Example:

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    gaussdb=# SELECT isfinite(timestamp '2001-02-16 21:28:30');
 isfinite 
----------
 t
(1 row)
gaussdb=# SELECT isfinite(timestamp 'infinity');
 isfinite 
----------
 f
(1 row)
  • isfinite(interval)

    Description: Checks whether the interval is a finite value. If yes, t is returned. Currently, f cannot be returned. If 'infinity' is entered, an error is reported.

    Return type: Boolean

    Example:

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

    Description: Specifies the system time when the current transaction starts.

    Return type: time

    Example:

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

    Description: Returns the system date and time when the current SQL query execution starts.

    Return type: timestamp

    Example:

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

    Description: Returns the system date and time when the current transaction starts. The results returned in the same transaction are the same.

    Return type: timestamp with time zone

    Example:

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

    Description: Returns the system date and time when the current SQL query execution starts.

    Return type: abstime

    Example:

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    gaussdb=# SELECT timenow();
        timenow
------------------------
 2020-06-23 20:36:56+08
(1 row)
  • dbtimezone

    Description: Time zone of the current database.

    Return type: text

    Example:

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    gaussdb=# SELECT dbtimezone;
        dbtimezone
------------------------
 PRC
(1 row)

    This function is valid only when the value of a_format_version is 10c and the value of a_format_dev_version is s2 in an A-compatible database.

  • 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 GUC parameter IntervalStyle to a to be compatible with the interval output format of the function.

    Return type: interval

    Example:

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    gaussdb=# SELECT numtodsinterval(100, 'HOUR');
 numtodsinterval 
-----------------
 100:00:00
(1 row)

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

    When a_format_version is set to 10c and a_format_dev_version is set to s2 in an A-compatible database, an error is reported if interval_unit is set to 'DAY' and num is set to a value greater than 1000000000.

  • numtoyminterval(num, interval_unit)

    Description: Converts a number to the interval type. num is a number of the numeric type, and interval_unit is a string of the fixed format ('YEAR'|'MONTH').

    You can set the GUC parameter IntervalStyle to a to be compatible with the interval output format of the function.

    Return type: interval

    Example:

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    gaussdb=# SELECT numtoyminterval(100, 'MONTH');
 numtoyminterval 
-----------------
 8 years 4 mons
(1 row)

gaussdb=# SET intervalstyle = oracle;
SET
gaussdb=# SELECT numtodsinterval(100, 'MONTH');
 numtoyminterval 
-----------------
 8-4
(1 row)

    This function is valid only when the value of a_format_version is 10c and the value of a_format_dev_version is s2 in an A-compatible database.

  • new_time(date, timezone1,timezone2)

    Description: Returns the date and time of the time zone specified by timezone2 when the date and time of the time zone specified by timezone1 are date.

    Return type: timestamp

    Example:

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    gaussdb=# SELECT new_time('1997-10-10','AST','EST');
      new_time       
---------------------
 1997-10-09 23:00:00
(1 row)
gaussdb=# SELECT NEW_TIME(TO_TIMESTAMP ('10-Sep-02 14:10:10.123000','DD-Mon-RR HH24:MI:SS.FF'), 'AST', 'PST');
        new_time         
-------------------------
 2002-09-10 10:10:10.123
(1 row)

    This function is valid only when the value of a_format_version is 10c and the value of a_format_dev_version is s2 in an A-compatible database.

  • sessiontimezone

    Description: Returns the time zone of the current session. There is no input parameter.

    Return type: text

    Example:

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    gaussdb=# SELECT SESSIONTIMEZONE;
 session_time_zone 
-------------------
 PST8PDT
(1 row)
gaussdb=# SELECT LOWER(SESSIONTIMEZONE);
   lower   
-----------
 @ 8 hours
(1 row)

    This function is valid only when the value of a_format_version is 10c and the value of a_format_dev_version is s2 in an A-compatible database.

    When the value of set session time zone is in the GMT+08:00/GMT-08:00 format, the verification fails and an error is reported. This behavior meets the expectation. If the value is 's2' and the "ERROR:invalid value for parameter "TimeZone" :"GMT-08:00"" error is reported when you use JDBC to create a connection, the application where the driver is located sends the same time zone parameter in GMT format to GaussDB. You can use either of the following methods to solve the problem:

    Method 1: Adjust the time zone of the OS on the application side and set the local time zone to the region format, for example, Asia/Shanghai.

    Method 2: Use the JDBC driver that matches the version on the application side. The JDBC driver changes the GMT time zone to a time zone format that can be identified by the database.

  • sys_extract_utc(timestamp| timestamptz)

    Description: Extracts Coordinated Universal Time (UTC, also formerly known as Greenwich Mean Time) from a date-time value with a time zone offset or time zone region name. If no time zone is specified, the date and time are associated with the session time zone. The input parameter can be in timestmp or timestamp format.

    Return type: timestamp

    Example:

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    gaussdb=# SELECT SYS_EXTRACT_UTC(TIMESTAMP '2000-03-28 11:30:00.00'); 
   sys_extract_utc   
---------------------
 2000-03-28 03:30:00
(1 row)
gaussdb=# SELECT SYS_EXTRACT_UTC(TIMESTAMPTZ '2000-03-28 11:30:00.00 -08:00'); 
   sys_extract_utc   
---------------------
 2000-03-28 19:30:00
(1 row)

    This function is valid only when the value of a_format_version is 10c and the value of a_format_dev_version is s2 in an A-compatible database.

  • tz_offset('time_zone_name' | '(+/-)hh:mi' | SESSIONTIMEZONE | DBTIMEZONE)

    Description: Returns the UTC offset of the time zone indicated by the input parameter. The input parameter has the preceding four formats.

    Return type: text

    Example:

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    gaussdb=# SELECT TZ_OFFSET('US/Pacific');
 tz_offset 
-----------
 -08:00
(1 row)
gaussdb=# SELECT TZ_OFFSET(sessiontimezone);
 tz_offset 
-----------
 +08:00
(1 row)

    This function is valid only when the value of a_format_version is 10c and the value of a_format_dev_version is s2 in an A-compatible database.

  • pg_sleep(seconds)

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

    Return type: void

    Example:

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    gaussdb=# SELECT pg_sleep(10);
 pg_sleep 
----------

(1 row)
  • statement_timestamp()

    Description: Current date and time (start of the current statement)

    Return type: timestamp with time zone

    Example:

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    gaussdb=# SELECT statement_timestamp();
      statement_timestamp      
-------------------------------
 2017-09-01 17:04:39.119267+08
(1 row)
  • sysdate

    Description: Returns the system date and time when the current SQL statement is executed.

    Return type: timestamp

    Example:

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

    Description: Returns the system date and time when the current SQL query execution starts.

    Return type: timestamp

    Example:

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    gaussdb=# SELECT current_sysdate();
   current_sysdate   
---------------------
 2023-06-20 20:09:02
(1 row)
  • timeofday()

    Description: Returns the timestamp (such as clock_timestamp, but the return type is text) of the system time when the current function is called.

    Return type: text

    Example:

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

    Description: Specifies the system date and time when the current transaction starts.

    Return type: timestamp with time zone

    Example:

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    gaussdb=# SELECT transaction_timestamp();
     transaction_timestamp     
-------------------------------
 2017-09-01 17:05:13.534454+08
(1 row)
  • add_months(d,n)

    Description: Returns the time point d plus n 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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    gaussdb=# 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)
    In the scenario where this function is in an A-compatible database, the value of a_format_version is 10c, and that of a_format_dev_version is s1:
    • If the calculation result is greater than 9999, an error is reported.
    • If the value of n is a decimal, the value is truncated instead of being rounded off.
  • last_day(d)

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

    Return type: timestamp

    Example:

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    gaussdb=# SELECT last_day(to_date('2017-01-01', 'YYYY-MM-DD')) AS cal_result;
     cal_result      
---------------------
 2017-01-31 00:00:00
(1 row)
  • months_between(d1, d2)

    Description: Calculates the month difference between time points d1 and d2. If both dates are the end of a month or are the same day, an integer is returned. Otherwise, the return value is a decimal and is calculated as 31 days per month.

    Return type: numeric

    Example:

    gaussdb=# SELECT months_between(to_date('2022-10-31', 'yyyy-mm-dd'), to_date('2022-09-30', 'yyyy-mm-dd'));
 months_between 
----------------
             1
(1 row)

gaussdb=# SELECT months_between(to_date('2022-10-30', 'yyyy-mm-dd'), to_date('2022-09-30', 'yyyy-mm-dd'));
 months_between 
----------------
             1
(1 row)

gaussdb=# SELECT months_between(to_date('2022-10-29', 'yyyy-mm-dd'), to_date('2022-09-30', 'yyyy-mm-dd'));
    months_between     
-----------------------
 .96774193548387096774
(1 row)

    This function is valid only when the value of a_format_version is 10c and the value of a_format_dev_version is s1 in an A-compatible database.

  • next_day(x,y)

    Description: Calculates the time of the next week y started from x.

    Return type: timestamp

    Example:

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    gaussdb=# 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:

    1
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    gaussdb=# 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:

    1
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    gaussdb=# 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)

    Return type: tinterval

    Return type: reltime

    Example:

    1
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3
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5
    		 
    gaussdb=# 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.

    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

    There are multiple methods for obtaining the current time. Select an appropriate API based on the actual service scenario.

    1. 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)
transaction_timestamp()
now()

      The values transferred by CURRENT_TIME and CURRENT_TIMESTAMP(precision) contain time zone information. The values transferred by LOCALTIME and LOCALTIMESTAMP do not contain time zone information. CURRENT_TIME, LOCALTIME, and LOCALTIMESTAMP can specify a precision parameter, which rounds the seconds field of the result to the 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.

      transaction_timestamp() is equivalent to CURRENT_TIMESTAMP(precision), indicating the start time of the transaction where the current statement is located. now() is equivalent to transaction_timestamp().

    2. The following APIs return the start time of the current statement: 
      statement_timestamp()

      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.

    3. The following APIs return the actual current time when the function is called: 
      clock_timestamp()
timeofday()

      clock_timestamp() returns the actual current time, and its value changes even in the same SQL statement. 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.

Table 2 shows the templates for truncating date/time values.

Table 2 Truncating date/time values

Item

Format

Description

Microsecond

MICROSECON

Truncates date/time values, accurate to the microsecond (000000–999999).

US

USEC

USECOND

Millisecond

MILLISECON

Truncates date/time values, accurate to the millisecond (000–999).

MS

MSEC

MSECOND

Second

S

Truncates date/time values, accurate to the second (00–59).

SEC

SECOND

Minute

M

Truncates date/time values, accurate to the minute (00–59).

MI

MIN

MINUTE

Hour

H

Truncates date/time values, accurate to the hour (00–23).

HH

HOUR

HR

Day

D

Truncates date/time values, accurate to the day (01-01 to 12–31)

DAY

DD

DDD

J

Week

W

Truncates date/time values, accurate to the week (the first day of the current week).

WEEK

Month

MM

Truncates date/time values, accurate to the month (the first day of the current month).

MON

MONTH

Quarter

Q

Truncates date/time values, accurate to the quarter (the first day of the current quarter).

QTR

QUARTER

Year

Y

Truncates date/time values, accurate to the year (the first day of the current year).

YEAR

YR

YYYY

Decade

DEC

Truncates date/time values, accurate to the decade (the first day of the current decade).

DECADE

Century

C

Truncates date/time values, accurate to the century (the first day of the current century).

CC

CENT

CENTURY

Millennium

MIL

Truncates date/time values, accurate to the millennium (the first day of the current millennium).

MILLENNIA

MILLENNIUM
Table 3 Parameters for time truncation and rounding

Item

Format

Description

Minute

M

Truncated or rounded off, accurate to minute (00–59).

MI

MIN

MINUTE

Hour

H

Truncated or rounded off, accurate to hour (00–23).

HH

HOUR

HR

HH12

HH24

Day

DD

Truncated or rounded off, accurate to day (01-01 to 12-31).

DDD

J

ISO week

IW

Truncated or rounded off, accurate to week (the first day of the week is Monday).

Week

DAY

Truncated or rounded off, accurate to week (the first day of the week is Sunday).

DY

D

Week of the month

W

Truncated or rounded off, accurate to week (the first day of the week is the first day of the month).

Week of the year

WW

Truncated or rounded off, accurate to week (the first day of the week is the first day of the year).

Month

MM

Truncated or rounded off, accurate to month (the first day of the month).

MON

MONTH

RM

Quarter

Q

Truncated or rounded off, accurate to quarter (the first day of the quarter).

QTR

QUARTER

Year

Y

Truncated or rounded off, accurate to year (the first day of the current year).

YEAR

YR

YYYY

SYYYY

YYY

YY

SYEAR

Decade

DEC

Truncated or rounded off, accurate to decade (the first day of the current decade).

DECADE

Century

C

Truncated or rounded off, accurate to the century (the first day of the century).

CC

CENT

CENTURY

SCC

Millennium

MIL

Truncated or rounded off, accurate to millennium (the first day of the millennium).

MILLENNIA

MILLENNIUM

The behaviors of Table 3 are valid only when the value of a_format_version is 10c and that of a_format_dev_version is s1 in an A-compatible database.

  • timestamp_diff(text, timestamp, timestamp)

    Description: Calculates the difference between two timestamps and truncates the difference to the precision specified by text.

    Return type: int64

    Example:

     1
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 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
    		 
    gaussdb=# SELECT timestamp_diff('year','2018-01-01','2020-04-01');
 timestamp_diff 
----------------
              2
(1 row)
gaussdb=# SELECT timestamp_diff('month','2018-01-01','2020-04-01');
 timestamp_diff 
----------------
             27
(1 row)
gaussdb=# SELECT timestamp_diff('quarter','2018-01-01','2020-04-01');
 timestamp_diff 
----------------
              9
(1 row)
gaussdb=# SELECT timestamp_diff('week','2018-01-01','2020-04-01');
 timestamp_diff 
----------------
            117
(1 row)
gaussdb=# SELECT timestamp_diff('day','2018-01-01','2020-04-01');
 timestamp_diff 
----------------
            821
(1 row)
gaussdb=# SELECT timestamp_diff('hour','2018-01-01 10:10:10','2018-01-01 12:12:12');
 timestamp_diff 
----------------
              2
(1 row)
gaussdb=# SELECT timestamp_diff('minute','2018-01-01 10:10:10','2018-01-01 12:12:12');
 timestamp_diff 
----------------
            122
(1 row)
gaussdb=# SELECT timestamp_diff('second','2018-01-01 10:10:10','2018-01-01 10:12:12');
 timestamp_diff 
----------------
            122
(1 row)
gaussdb=# SELECT timestamp_diff('microsecond','2018-01-01 10:10:10','2018-01-01 10:12:12');
 timestamp_diff 
----------------
      122000000
(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 equivalent to timestamp_diff(text, timestamp, timestamp).

This function is valid only when GaussDB is compatible with the MY type (that is, dbcompatibility = 'B').

  • year

    Year.

    1
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5
    		 
    gaussdb=#  SELECT TIMESTAMPDIFF(YEAR, '2018-01-01', '2020-01-01');
 timestamp_diff
----------------
              2
(1 row)
  • quarter

    Quarter.

    1
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3
4
5
    		 
    gaussdb=#  SELECT TIMESTAMPDIFF(QUARTER, '2018-01-01', '2020-01-01');
 timestamp_diff
----------------
              8
(1 row)
  • month

    Month.

    1
2
3
4
5
    		 
    gaussdb=#  SELECT TIMESTAMPDIFF(MONTH, '2018-01-01', '2020-01-01');
 timestamp_diff
----------------
             24
(1 row)
  • week

    Week.

    1
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3
4
5
    		 
    gaussdb=#  SELECT TIMESTAMPDIFF(WEEK, '2018-01-01', '2020-01-01');
 timestamp_diff
----------------
            104
(1 row)
  • day
    Day. 
    1
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3
4
5
    		 
    gaussdb=#  SELECT TIMESTAMPDIFF(DAY, '2018-01-01', '2020-01-01');
 timestamp_diff
----------------
            730
(1 row)
  • hour

    Hour.

    1
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3
4
5
    		 
    gaussdb=#  SELECT TIMESTAMPDIFF(HOUR, '2020-01-01 10:10:10', '2020-01-01 11:11:11');
 timestamp_diff
----------------
              1
(1 row)
  • minute

    Minute.

    1
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3
4
5
    		 
    gaussdb=#  SELECT TIMESTAMPDIFF(MINUTE, '2020-01-01 10:10:10', '2020-01-01 11:11:11');
 timestamp_diff
----------------
             61
(1 row)
  • second

    Second.

    1
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3
4
5
    		 
    gaussdb=#  SELECT TIMESTAMPDIFF(SECOND, '2020-01-01 10:10:10', '2020-01-01 11:11:11');
 timestamp_diff
----------------
           3661
(1 row)
  • microseconds

    The second field, including fractional parts, is multiplied by 1,000,000.

    1
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3
4
5
    		 
    gaussdb=#  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 
    1
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5
    		 
    gaussdb=# 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 fields such as year or hour from date/time values. source must be a value expression of the date type (timestamp, time, or interval). field is an identifier or string that selects what field to extract from the source value. The extract function returns a value of the double precision type. 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.

    1
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5
    		 
    gaussdb=# 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) field (1–31) 
      1
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3
4
5
      		 
      gaussdb=# SELECT EXTRACT(DAY FROM TIMESTAMP '2001-02-16 20:38:40');
 date_part 
-----------
        16
(1 row)
    • For interval values, the number of days 
      1
2
3
4
5
      		 
      gaussdb=# SELECT EXTRACT(DAY FROM INTERVAL '40 days 1 minute');
 date_part 
-----------
        40
(1 row)
  • decade

    Year divided by 10

    1
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3
4
5
    		 
    gaussdb=# 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
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3
4
5
    		 
    gaussdb=# 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
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3
4
5
    		 
    gaussdb=# 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.

      1
2
3
4
5
      		 
      gaussdb=# 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
      		 
      gaussdb=# SELECT EXTRACT(EPOCH FROM INTERVAL '5 days 3 hours');
 date_part 
-----------
    442800
(1 row)
    • Way to convert an epoch value back to a timestamp 
      1
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4
5
      		 
      gaussdb=# 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 (0–23)

    1
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3
4
5
    		 
    gaussdb=# 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.

    1
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3
4
5
    		 
    gaussdb=# 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 week for more information.

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 5
 6
 7
 8
 9
10
    		 
    gaussdb=# SELECT EXTRACT(ISOYEAR FROM DATE '2006-01-01');
 date_part 
-----------
      2005
(1 row)
gaussdb=# SELECT EXTRACT(WEEK FROM TIMESTAMP '2006-01-01 00:00:40');
 date_part
-----------
        52
(1 row)

    gaussdb=# SELECT EXTRACT(ISOYEAR FROM DATE '2006-01-02');
 date_part 
-----------
      2006
(1 row)
gaussdb=# SELECT EXTRACT(WEEK FROM TIMESTAMP '2006-01-02 00:00:40');
 date_part
-----------
         1
(1 row)
  • microseconds

    The second field, including fractional parts, is multiplied by 1,000,000.

    1
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3
4
5
    		 
    gaussdb=# 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
    		 
    gaussdb=# SELECT EXTRACT(MILLENNIUM FROM TIMESTAMP '2001-02-16 20:38:40');
 date_part 
-----------
         3
(1 row)
  • milliseconds

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

    1
2
3
4
5
    		 
    gaussdb=# SELECT EXTRACT(MILLISECONDS FROM TIME '17:12:28.5');
 date_part 
-----------
     28500
(1 row)
  • minute

    Minute (0–59).

    1
2
3
4
5
    		 
    gaussdb=# 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
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3
4
5
    		 
    gaussdb=# 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
    		 
    gaussdb=# 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
    		 
    gaussdb=# SELECT EXTRACT(QUARTER FROM TIMESTAMP '2001-02-16 20:38:40');
 date_part 
-----------
         1
(1 row)
  • second

    Second field, including fractional parts (0–59).

    1
2
3
4
5
    		 
    gaussdb=# 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. 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, 2006-01-01 is the 52nd week of 2005, and 2006-01-02 is the first week of 2006. You are advised to use the columns isoyear and week together to ensure consistency.

     1
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 4
 5
 6
 7
 8
 9
10
    		 
    gaussdb=# SELECT EXTRACT(ISOYEAR FROM DATE '2006-01-01');
 date_part 
-----------
      2005
(1 row)
gaussdb=# SELECT EXTRACT(WEEK FROM TIMESTAMP '2006-01-01 00:00:40');
 date_part
-----------
        52
(1 row)

    gaussdb=# SELECT EXTRACT(ISOYEAR FROM DATE '2006-01-02');
 date_part 
-----------
      2006
(1 row)
gaussdb=# SELECT EXTRACT(WEEK FROM TIMESTAMP '2006-01-02 00:00:40');
 date_part
-----------
         1
(1 row)
  • year

    Year field.

    1
2
3
4
5
    		 
    gaussdb=# 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 are the same as those for extract. For details, see EXTRACT.

Example:

1
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3
4
5
 
gaussdb=# SELECT date_part('day', TIMESTAMP '2001-02-16 20:38:40');
 date_part 
-----------
        16
(1 row)

1
2
3
4
5
 
gaussdb=# SELECT date_part('hour', INTERVAL '4 hours 3 minutes');
 date_part 
-----------
         4
(1 row)

Table 4 specifies the schema for formatting date and time values.

Table 4 Schema for formatting date and time

Category

Format

Description

Hour

HH

Number of hours in one day (01–12)

HH12

Number of hours in one day (01–12)

HH24

Number of hours in one day (00–23)

Minute

MI

Minute (00–59)

Second

SS

Second (00–59)

FF

Microsecond (000000–999999)

FF1

Microsecond (0-9)

FF2

Microsecond (00-99)

FF3

Microsecond (000-999)

FF4

Microsecond (0000-9999)

FF5

Microsecond (00000-99999)

FF6

Microsecond (000000–999999)

SSSSS

Second after midnight (0–86399)

Morning and afternoon

AM or A.M.

Morning identifier

PM or P.M.

Afternoon identifier

Year

Y,YYY

Year with comma (with four digits or more)

SYYYY

Year with four digits BC

YYYY

Year (with four digits or more)

YYY

Last three digits of a year

YY

Last two digits of a year

Y

Last one digit of a year

IYYY

ISO year (with four digits or more)

IYY

Last three digits of an ISO year

IY

Last two digits of an ISO year

I

Last one digit of an ISO year

RR

Last two digits of a year (A year of the 20th century can be stored in the 21st century.)

RRRR

Capable of receiving a year with four digits or two digits. If there are 2 digits, the value is the same as the returned value of RR. If there are 4 digits, the value is the same as YYYY.
  • BC or B.C.
  • AD or A.D.

Era indicator BC or AD

Month

MONTH

Full spelling of a month in uppercase (9 characters are filled in if the value is empty.)

MON

Month in abbreviated format in uppercase (with three characters)

MM

Month (01–12)

RM

Month in Roman numerals (I–XII; I=JAN) and uppercase

Day

DAY

Full spelling of a date in uppercase (9 characters are filled in if the value is empty.)

DY

Day in abbreviated format in uppercase (with three characters)

DDD

Day in a year (001–366)

DD

Day in a month (01–31)

D

Day in a week (1–7).

Week

W

Week in a month (1–5) (The first week starts from the first day of the month.)

WW

Week in a year (1–53) (The first week starts from the first day of the year.)

IW

Week in an ISO year (The first Thursday is in the first week.)

Century

CC

Century (with two digits) (The 21st century starts from 2001-01-01.)

Julian date

J

Julian date (starting from January 1 of 4712 BC)

Quarter

Q

Quarter
When a_format_version is set to 10c and a_format_dev_version is set to s1 in an A-compatible database, the date and time will be formatted in the specified pattern.
Table 5 New formats for formatting date and time

Item

Format

Description

Century

SCC

Century. A hyphen (-) will be displayed before BC years.

Year

SYYYY

Returns a numeric year. A hyphen (-) will be displayed before BC years.

RR

Returns the two-digit year of a date.

RRRR

Returns the four-digit year of a date.

YEAR

Returns the year of the character type.

SYEAR

Returns the year of the character type. A hyphen (-) will be displayed before BC years.

Date Format

DL

Returns the date in the specified long date format.

DS

Returns the date in the specified short date format.

TS

Returns the time in the specified time format.

Second

FF7

Microsecond (0000000-9999990)

FF8

Microsecond (00000000-99999900)

FF9

Microsecond (000000000-999999000)

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 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.

In the scenario where this function is in an A-compatible database, the value of a_format_version is 10c, and that of a_format_dev_version is s1:
  • The to_date and to_timestamp functions support the FX pattern (the input strictly corresponds to a pattern) and the X pattern (decimal point).
  • The input pattern can appear only once, indicating that the patterns of the same information cannot appear at the same time. For example, SYYYY and BC cannot be used together.
  • The pattern is case insensitive.
  • You are advised to use a separator between the input and the pattern. Otherwise, the behavior may not be compatible with database O.
Parent topic: Functions and Operators