PostgreSQL 7.1.3 Documentation
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# 4.7. Date/Time Functions

Table 4-14 shows the available functions for date/time value processing. The basic arithmetic operators (`+`, `*`, etc.) are also available. For formatting functions, refer to Section 4.6. You should be familiar with the background information on date/time data types (see Section 3.4).

Table 4-14. Date/Time Functions

Name | Return Type | Description | Example | Result
--- | --- | --- | --- | ---
age(timestamp) | interval | Subtract from today | age(timestamp '1957-06-13') | 43 years 8 mons 3 days
age(timestamp, timestamp) | interval | Subtract arguments | age('2001-04-10', timestamp '1957-06-13') | 43 years 9 mons 27 days
current_date | date | Today's date; see below |  |
current_time | time | Time of day; see below |  |
current_timestamp | timestamp | date and time; see also below |  |
date_part(text, timestamp) | double precision | Get subfield (equivalent to `extract`); see also below | date_part('hour', timestamp '2001-02-16 20:38:40') | 20
date_part(text, interval) | double precision | Get subfield (equivalent to `extract`); see also below | date_part('month', interval '2 years 3 months') | 3
date_trunc(text, timestamp) | timestamp | Truncate to specified precision; see also below | date_trunc('hour', timestamp '2001-02-16 20:38:40') | 2001-02-16 20:00:00+00
extract(`field` from timestamp) | double precision | Get subfield; see also below | extract(hour from timestamp '2001-02-16 20:38:40') | 20
extract(`field` from interval) | double precision | Get subfield; see also below | extract(month from interval '2 years 3 months') | 3
isfinite(timestamp) | boolean | Test for finite time stamp (neither invalid nor infinity) | isfinite(timestamp '2001-02-16 21:28:30') | true
isfinite(interval) | boolean | Test for finite interval | isfinite(interval '4 hours') | true
now() | timestamp | Current date and time (equivalent to `current_timestamp`); see also below |  |
timeofday() | text | High-precision date and time; see also below | timeofday() | Wed Feb 21 17:01:13.000126 2001 EST
timestamp(date) | timestamp | Date to timestamp | timestamp(date '2000-12-25') | 2000-12-25 00:00:00
timestamp(date, time) | timestamp | Date and time to a timestamp | timestamp(date '1998-02-24',time '23:07') | 1998-02-24 23:07:00

## 4.7.1. `EXTRACT`, `date_part`

    EXTRACT (field FROM source)

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

century

  The year field divided by 100

      SELECT EXTRACT(CENTURY FROM TIMESTAMP '2001-02-16 20:38:40');
      Result: 20

  Note that the result for the century field is simply the year field divided by 100, and not the conventional definition which puts most years in the 1900's in the twentieth century.

day

  The day (of the month) field (1 - 31)

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

decade

  The year field divided by 10

      SELECT EXTRACT(DECADE FROM TIMESTAMP '2001-02-16 20:38:40');
      Result: 200

dow

  The day of the week (0 - 6; Sunday is 0) (for `timestamp` values only)

      SELECT EXTRACT(DOW FROM TIMESTAMP '2001-02-16 20:38:40');
      Result: 5

doy

  The day of the year (1 - 365/366) (for `timestamp` values only)

      SELECT EXTRACT(DOY FROM TIMESTAMP '2001-02-16 20:38:40');
      Result: 47

epoch

  For `date` and `timestamp` values, the number of seconds since 1970-01-01 00:00:00 (Result may be negative.); for `interval` values, the total number of seconds in the interval

      SELECT EXTRACT(EPOCH FROM TIMESTAMP '2001-02-16 20:38:40');
      Result: 982352320

      SELECT EXTRACT(EPOCH FROM INTERVAL '5 days 3 hours');
      Result: 442800

hour

  The hour field (0 - 23)

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

microseconds

  The seconds field, including fractional parts, multiplied by 1 000 000. Note that this includes full seconds.

      SELECT EXTRACT(MICROSECONDS FROM TIME '17:12:28.5');
      Result: 28500000

millennium

  The year field divided by 1000

      SELECT EXTRACT(MILLENNIUM FROM TIMESTAMP '2001-02-16 20:38:40');
      Result: 2

  Note that the result for the millennium field is simply the year field divided by 1000, and not the conventional definition which puts years in the 1900's in the second millennium.

milliseconds

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

      SELECT EXTRACT(MILLISECONDS FROM TIME '17:12:28.5');
      Result: 28500

minute

  The minutes field (0 - 59)

      SELECT EXTRACT(MINUTE FROM TIMESTAMP '2001-02-16 20:38:40');
      Result: 38

month

  For `timestamp` values, the number of the month within the year (1 - 12) ; for `interval` values the number of months, modulo 12 (0 - 11)

      SELECT EXTRACT(MONTH FROM TIMESTAMP '2001-02-16 20:38:40');
      Result: 2

      SELECT EXTRACT(MONTH FROM INTERVAL '2 years 3 months');
      Result: 3

      SELECT EXTRACT(MONTH FROM INTERVAL '2 years 13 months');
      Result: 1

quarter

  The quarter of the year (1 - 4) that the day is in (for `timestamp` values only)

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

second

  The seconds field, including fractional parts (0 - 59[1])

      SELECT EXTRACT(SECOND FROM TIMESTAMP '2001-02-16 20:38:40');
      Result: 40

      SELECT EXTRACT(SECOND FROM TIME '17:12:28.5');
      Result: 28.5

week

  From a `timestamp` value, calculate 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 week starts on Monday.) In other words, the first Thursday of a year is in week 1 of that year.

      SELECT EXTRACT(WEEK FROM TIMESTAMP '2001-02-16 20:38:40');
      Result: 7

year

  The year field

      SELECT EXTRACT(YEAR FROM TIMESTAMP '2001-02-16 20:38:40');
      Result: 2001

The `extract` function is primarily intended for computational processing. For formatting date/time values for display, see Section 4.6.

The `date_part` function is modeled on the traditional Ingres equivalent to the SQL-function `extract`:

    date_part('field', source)

Note that here the `field` value needs to be a string. The valid field values for `date_part` are the same as for `extract`.

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

    SELECT date_part('hour', INTERVAL '4 hours 3 minutes')
    Result: 4

## 4.7.2. `date_trunc`

The function `date_trunc` is conceptually similar to the `trunc` function for numbers.

    date_trunc('field', source)

`source` is a value expression of type `timestamp` (values of type `date` and `time` are cast automatically). `field` selects to which precision to truncate the time stamp value. The return value is of type `timestamp` with all fields that are less than the selected one set to zero (or one, for day and month).

Valid values for `field` are:

microseconds
milliseconds
second
minute
hour
day
month
year
decade
century
millennium

    SELECT date_trunc('hour', TIMESTAMP '2001-02-16 20:38:40');
    Result: 2001-02-16 20:00:00+00

    SELECT date_trunc('year', TIMESTAMP '2001-02-16 20:38:40');
    Result: 2001-01-01 00:00:00+00

## 4.7.3. Current Date/Time

The following functions are available to obtain the current date and/or time:

    CURRENT_TIME
    CURRENT_DATE
    CURRENT_TIMESTAMP

Note that because of the requirements of the SQL standard, these functions must not be called with trailing parentheses.

    SELECT CURRENT_TIME;
    19:07:32

    SELECT CURRENT_DATE;
    2001-02-17

    SELECT CURRENT_TIMESTAMP;
    2001-02-17 19:07:32-05

The function `now()` is the traditional Postgres equivalent to `CURRENT_TIMESTAMP`.

There is also `timeofday()`, which returns current time to higher precision than the `CURRENT_TIMESTAMP` family does:

    SELECT timeofday();
     Sat Feb 17 19:07:32.000126 2001 EST

`timeofday()` uses the operating system call `gettimeofday(2)`, which may have resolution as good as microseconds (depending on your platform); the other functions rely on `time(2)` which is restricted to one-second resolution. For historical reasons, `timeofday()` returns its result as a text string rather than a timestamp value.

It is quite important to realize that `CURRENT_TIMESTAMP` and related functions all return the time as of the start of the current transaction; their values do not increment while a transaction is running. But `timeofday()` returns the actual current time.

All the date/time datatypes also accept the special literal value `now` to specify the current date and time. Thus, the following three all return the same result:

    SELECT CURRENT_TIMESTAMP;
    SELECT now();
    SELECT TIMESTAMP 'now';

> Note: You do not want to use the third form when specifying a DEFAULT value while creating a table. The system will convert `now` to a timestamp as soon as the constant is parsed, so that when the default value is needed, the time of the table creation would be used! The first two forms will not be evaluated until the default value is used, because they are function calls. Thus they will give the desired behavior of defaulting to the time of row insertion.

### Notes

[1] | 60 if leap seconds are implemented by the operating system

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