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Date and Time Processing Functions and Operators

Date and Time Operators

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

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

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

Operators

Examples

+

SELECT date '2001-09-28' + integer '7' AS RESULT;
       result        
---------------------
 2001-10-05 00:00:00
(1 row)
SELECT date '2001-09-28' + interval '1 hour' AS RESULT;
       result        
---------------------
 2001-09-28 01:00:00
(1 row)
SELECT date '2001-09-28' + time '03:00' AS RESULT;
       result        
---------------------
 2001-09-28 03:00:00
(1 row)
SELECT interval '1 day' + interval '1 hour' AS RESULT;
     result     
----------------
 1 day 01:00:00
(1 row)
SELECT timestamp '2001-09-28 01:00' + interval '23 hours' AS RESULT;
       result        
---------------------
 2001-09-29 00:00:00
(1 row)
SELECT time '01:00' + interval '3 hours' AS RESULT;
  result  
----------
 04:00:00
(1 row)

-

SELECT date '2001-10-01' - date '2001-09-28' AS RESULT;
 result 
--------
 3 days
(1 row)
SELECT date '2001-10-01' - integer '7' AS RESULT;
       result        
---------------------
 2001-09-24 00:00:00
(1 row)
SELECT date '2001-09-28' - interval '1 hour' AS RESULT;
       result        
---------------------
 2001-09-27 23:00:00
(1 row)
SELECT time '05:00' - time '03:00' AS RESULT;
  result  
----------
 02:00:00
(1 row)
SELECT time '05:00' - interval '2 hours' AS RESULT;
  result  
----------
 03:00:00
(1 row)
SELECT timestamp '2001-09-28 23:00' - interval '23 hours' AS RESULT;
       result        
---------------------
 2001-09-28 00:00:00
(1 row)
SELECT interval '1 day' - interval '1 hour' AS RESULT;
  result  
----------
 23:00:00
(1 row)
SELECT timestamp '2001-09-29 03:00' - timestamp '2001-09-27 12:00' AS RESULT;
     result     
----------------
 1 day 15:00:00
(1 row)

*

SELECT 900 * interval '1 second' AS RESULT;
  result  
----------
 00:15:00
(1 row)
SELECT 21 * interval '1 day' AS RESULT;
 result  
---------
 21 days
(1 row)
SELECT double precision '3.5' * interval '1 hour' AS RESULT;
  result  
----------
 03:30:00
(1 row)

/

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

Time/Date functions

  • age(timestamp, timestamp)

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

    Return type: interval

    For example:

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

    Description: Subtracts from current_date

    Return type: interval

    For example:

    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

    For example:

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

    Description: Current date

    Return type: date

    For example:

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

    Description: Current time

    Return type: time with time zone

    For example:

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

    Description: Specifies the current date and time.

    Return type: timestamp with time zone

    For example:

    SELECT current_timestamp;
           pg_systimestamp        
    ------------------------------
     2017-09-01 16:58:19.22173+08
    (1 row)
  • date_part(text, timestamp)

    Description:

    Description: Obtains the hour.

    Equivalent to extract(field from timestamp).

    Return type: double precision

    For example:

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

    Description:

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

    Equivalent to extract(field from timestamp).

    Return type: double precision

    For example:

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

    Description: Truncates to the precision specified by text.

    Return type: timestamp

    For example:

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

    Description: Obtains the hour.

    Return type: double precision

    For example:

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

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

    Return type: double precision

    For example:

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

    Description: Tests for valid date.

    Return type: Boolean

    For example:

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

    Description: Tests for valid timestamp.

    Return type: Boolean

    For example:

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

    Description: Tests for valid interval.

    Return type: Boolean

    For example:

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

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

    Return type: interval

    For example:

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

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

    Return type: interval

    For example:

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

    Description: Adjusts interval using justify_days and justify_hours.

    Return type: interval

    For example:

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

    Description: Current time

    Return type: time

    For example:

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

    Description: Specifies the current date and time.

    Return type: timestamp

    For example:

    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

    For example:

    SELECT now();
                  now              
    -------------------------------
     2017-09-01 17:03:42.549426+08
    (1 row)
  • numtodsinterval(num, interval_unit)

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

    For example:

    SELECT numtodsinterval(100, 'HOUR');
     numtodsinterval 
    -----------------
     100:00:00
    (1 row)
  • pg_sleep(seconds)

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

    Return type: void

    For example:

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

    Description: Specifies the current date and time.

    Return type: timestamp with time zone

    For example:

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

    Description: Specifies the current date and time.

    Return type: timestamp

    For example:

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

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

    Return type: text

    For example:

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

    Description: Current date and time (equivalent to current_timestamp)

    Return type: timestamp with time zone

    For example:

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

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

    Return type: timestamp

    For example:

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

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

    Return type: timestamp

    For example:

    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

    For example:

    postgres=# select next_day(timestamp '2017-05-25 00:00:00','Sunday')AS cal_result;
         cal_result      
    ---------------------
     2017-05-28 00:00:00
    (1 row)

EXTRACT

EXTRACT(field FROM source)

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

  • century

    Century

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

    For example:

    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)
      SELECT EXTRACT(DAY FROM TIMESTAMP '2001-02-16 20:38:40');
       date_part 
      -----------
              16
      (1 row)
    • For interval values, the number of days
      SELECT EXTRACT(DAY FROM INTERVAL '40 days 1 minute');
       date_part 
      -----------
              40
      (1 row)
  • decade

    Year column divided by 10

    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)

    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)

    SELECT EXTRACT(DOY FROM TIMESTAMP '2001-02-16 20:38:40');
     date_part 
    -----------
            47
    (1 row)
  • epoch
    • For timestamp with time zone values, the number of seconds since 1970-01-01 00:00:00 UTC (can be negative);

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

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

      SELECT EXTRACT(EPOCH FROM TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40.12-08');
        date_part   
      --------------
       982384720.12
      (1 row)
      SELECT EXTRACT(EPOCH FROM INTERVAL '5 days 3 hours');
       date_part 
      -----------
          442800
      (1 row)
    • Way to convert an epoch value back to a timestamp
      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)

    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.

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

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

    Each ISO year begins with the Monday of the week containing the 4th of January, so in early January or late December the ISO year may be different from the Gregorian year. See the week column for more information.

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

      

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

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

    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.

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

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

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

    Minutes column (0–59)

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

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

    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)

    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

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

    Seconds column, including fractional parts (0–59)

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

    The time zone offset from UTC, measured in seconds. Positive values correspond to time zones east of UTC, negative values to zones west of UTC.

  • timezone_hour

    The hour component of the time zone offset

  • timezone_minute

    The minute component of the time zone offset

  • week

    The number of the week of the year that the day is in. By definition (ISO 8601), the first week of a year contains January 4 of that year. (The ISO-8601 week starts on Monday.) In other words, the first Thursday of a year is in week 1 of that year.

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

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

    Year column

    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.

For example:

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

Category

Format

Description

Hours

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)

Seconds

SS

Second (00-59)

FF

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 a 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 Before Christ (BC) and After Christ (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

NOTE:

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.