Lu, Huayi a24ca60074 DWS DEVELOPER 811 version

Reviewed-by: Hasko, Vladimir <vladimir.hasko@t-systems.com>
Co-authored-by: Lu, Huayi <luhuayi@huawei.com>
Co-committed-by: Lu, Huayi <luhuayi@huawei.com>

2023-01-19 13:37:49 +00:00

167 KiB

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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.

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SELECT date '2001-10-01' - '7' AS RESULT;

Table 1 Time and date operators

Operators

Examples

Add a date with an integer to obtain the date after 7 days.

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SELECT date '2001-09-28' + integer '7' AS RESULT;
       result        
---------------------
 2001-10-05 00:00:00
(1 row)

Add a date with an interval to obtain the time after 1 hour.

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SELECT date '2001-09-28' + interval '1 hour' AS RESULT;
       result        
---------------------
 2001-09-28 01:00:00
(1 row)

Add a date with a time to obtain a specific time.

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

Add a date with an interval to obtain the time after one month.

If the sum or subtraction results fall beyond the date range of a month, the result will be rounded to the last day of the month.

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SELECT date '2021-01-31' + interval '1 month' AS RESULT;
       result
---------------------
 2021-02-28 00:00:00
(1 row)

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SELECT date '2021-02-28' + interval '1 month' AS RESULT;
       result
---------------------
 2021-03-28 00:00:00
(1 row)

Add two intervals to obtain the sum.

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

Add a timestamp with an interval to obtain the time after 23 hours.

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

Add a time with an interval to obtain the time after three hours.

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

Subtract a date from another to obtain the difference.

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

Subtract an integer from a date, the return is a timestamp type.

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

Subtract an interval from a date to obtain the time difference.

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

Subtract a time from another time to obtain the time difference.

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

Subtract an interval from a time to obtain the time difference.

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

Subtract an interval from a timestamp to obtain the date difference.

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

Subtract an interval from another interval to obtain the time difference.

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

Subtract a timestamp from another timestamp to obtain the time difference.

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

Obtain the time at the previous day.

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select now() - interval '1 day'AS RESULT;
           result
-------------------------------
 2022-08-08 01:46:15.555406+00
(1 row)

Multiply an interval by a quantity:

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

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

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

Divide an interval by a quantity to obtain a time segment.

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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:
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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:

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

timestampdiff(field, timestamp1, timestamp2)
Description: Subtracts timestamp1 from timestamp2 and returns the difference in the unit of field. If the difference is negative, this function returns it normally. The field can be day, month, quarter, day, week, hour, minute, second, or microsecond.

Return type: bigint

For example:
```
SELECT timestampdiff(day, timestamp '2001-02-01', timestamp '2003-05-01 12:05:55');
 timestampdiff 
---------------
      819
(1 row)
```

clock_timestamp()

Description: Specifies the current timestamp of the real-time clock.

Return type: timestamp with time zone

For example:

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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:

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

current_time

Description: Current time

Return type: time with time zone

For example:

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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:

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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:
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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:
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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:

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

trunc(timestamp)

Description: By default, the data is intercepted by day.

For example:

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

extract(field from timestamp)

Description: Obtains the hour.

Return type: double precision

For example:

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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:
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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:

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

isfinite(timestamp)

Description: Tests for valid timestamp.

Return type: boolean

For example:

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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:

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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:
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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:
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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:

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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:

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

localtimestamp

Description: Specifies the current date and time.

Return type: timestamp

For example:

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

now()

Description: Timestamp indicating the start of the current transaction.

Return type: timestamp with time zone

For example:

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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'

You can set the IntervalStyle parameter to oracle to be compatible with the interval output format of the function in the Oracle database.

For example:

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

SET intervalstyle = oracle;
SET
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

For example:
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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:

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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:

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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:

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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:

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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:

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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.
- In the ORA- or TD-compatible mode, the return type is timestamp.
- In the MySQL-compatible mode, the return type is date.
For example:
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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
- In the ORA- or TD-compatible mode, the return type is timestamp.
- In the MySQL-compatible mode, the return type is date.
For example:
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select next_day(timestamp '2017-05-25 00:00:00','Sunday')AS cal_result; cal_result --------------------- 2017-05-28 00:00:00 (1 row)
to_days(timestamp)
Description: Returns the number of days from the first day of year 0 to a specified date.

Return type: int

For example:
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SELECT to_days(timestamp '2008-10-07'); to_days --------- 733687 (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:
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SELECT EXTRACT(CENTURY FROM TIMESTAMP '2000-12-16 12:21:13'); date_part ----------- 20 (1 row)

day

For timestamp values, the day (of the month) column (1–31)

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

For interval values, the number of days

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

decade

Year column divided by 10

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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)

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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)

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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.

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

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SELECT EXTRACT(EPOCH FROM INTERVAL '5 days 3 hours');
 date_part 
-----------
    442800
(1 row)

Way to convert an epoch value back to a timestamp

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SELECT TIMESTAMP WITH TIME ZONE 'epoch' + 982384720.12 * INTERVAL '1 second' AS RESULT;
          result          
---------------------------
 2001-02-17 12:38:40.12+08
(1 row)

hour

Hour column (0–23)

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

isodow

Day of the week (1–7)

Monday is 1 and Sunday is 7.

This is identical to dow except for Sunday.

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

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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.

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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.

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

minute

Minutes column (0–59)

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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);

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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)

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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

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

second

Seconds column, including fractional parts (0–59)

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

year

Year column

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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 the field must be a string, rather than a name. The valid field names are the same as those for extract. For details, see EXTRACT.

For example:

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

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

date_format

date_format(timestamp, fmt)

Converts a date into a string in the format specified by fmt.

For example:

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SELECT date_format('2009-10-04 22:23:00', '%M %D %W');
    date_format
--------------------
 October 4th Sunday
(1 row)
SELECT date_format('2021-02-20 08:30:45', '%Y-%m-%d %H:%i:%S');
     date_format
---------------------
 2021-02-20 08:30:45
(1 row)
SELECT date_format('2021-02-20 18:10:15', '%r-%T');
     date_format
----------------------
 06:10:15 PM-18:10:15
(1 row)

The following table describes the patterns of date parameter values. They can be used for the date_format, time_format, str_to_date, str_to_time, and from_unixtime functions.

**Table 2** Output formats of date_format
Format	Description	Value
%a	Abbreviated week name	Sun...Sat
%b	Abbreviated month name	Jan...Dec
%c	Month	0...12
%D	Date with a suffix	0th, 1st, 2nd, 3rd, ...
%d	Day in a month (two digits)	00...31
%e	Day in a month	0...31
%f	Microsecond	000000...999999
%H	Hour, in 24-hour format	00...23
%h	Hour, in 12-hour format	01...12
%I	Hour, in 12-hour format, same as %h	01...12
%i	Minute	00...59
%j	Day in a year	001...366
%k	Hour, in 24-hour format, same as %H	0...23
%l	Hour, in 12-hour format, same as %h	1...12
%M	Month name	January...December
%m	Month (two digits)	00...12
%p	Morning and afternoon	AM PM
%r	Time, in 12-hour format	hh::mm::ss AM/PM
%S	Second	00...59
%s	Second, same as %S	00...59
%T	Time, in 24-hour format	hh::mm::ss
%U	Week (Sunday is the first day of a week)	00...53
%u	Week (Monday is the first day of a week)	00...53
%V	Week (Sunday is the first day of a week). It is used together with %X.	01...53
%v	Week (Monday is the first day of a week). It is used together with %x.	01...53
%W	Week name	Sunday...Saturday
%w	Day of a week. The value is 0 for Sunday.	0...6
%X	Year (four digits). It is used together with %V. Sunday is the first day of a week.	-
%x	Year (four digits). It is used together with %v. Monday is the first day of a week.	-
%Y	Year (four digits)	-
%y	Year (two digits)	-
%%	Character '%'	Character '%'
%x	'x': any character apart from the preceding ones	Character 'x'

In the preceding table, %U, %u, %V, %v, %X, and %x are not supported currently.

Parent topic: Functions and Operators

167 KiB Raw Permalink Blame History Unescape Escape

Date and Time Processing Functions and Operators

Date and Time Operators

Time/Date functions

EXTRACT

date_part

date_format

167 KiB

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