PostgreSQL User's Guide
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# Date/Time Functions

The date/time functions provide a powerful set of tools for manipulating various date/time types.

Table 5-6. Date/Time Functions

Function | Returns | Description | Example
--- | --- | --- | ---
abstime(timestamp) | abstime | convert to abstime | abstime(timestamp 'now')
age(timestamp) | interval | preserve months and years | age(timestamp '1957-06-13')
age(timestamp,timestamp) | interval | preserve months and years | age('now', timestamp '1957-06-13')
date_part(text,timestamp) | float8 | portion of date | date_part('dow',timestamp 'now')
date_part(text,interval) | float8 | portion of time | date_part('hour',interval '4 hrs 3 mins')
date_trunc(text,timestamp) | timestamp | truncate date | date_trunc('month',abstime 'now')
interval(reltime) | interval | convert to interval | interval(reltime '4 hours')
isfinite(timestamp) | bool | a finite time? | isfinite(timestamp 'now')
isfinite(interval) | bool | a finite time? | isfinite(interval '4 hrs')
reltime(interval) | reltime | convert to reltime | reltime(interval '4 hrs')
timestamp(date) | timestamp | convert to timestamp | timestamp(date 'today')
timestamp(date,time) | timestamp | convert to timestamp | timestamp(timestamp '1998-02-24',time '23:07');
to_char(timestamp,text) | text | convert to string | to_char(timestamp '1998-02-24','DD');

For the `date_part` and `date_trunc` functions, arguments can be ``year`', ``month`', ``day`', ``hour`', ``minute`', and ``second`', as well as the more specialized quantities ``decade`', ``century`', ``millennium`', ``millisecond`', and ``microsecond`'. `date_part` allows ``dow`' to return day of week, '`week`' to return the ISO-defined week of year, and ``epoch`' to return seconds since 1970 (for timestamp) or '`epoch`' to return total elapsed seconds (for interval).

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