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).