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The function DATE_TRUNC is conceptually similar to the TRUNC function for numbers. The return value is of type timestamp or interval with all fields that are less significant than the selected one set to zero (or one, for day and month).
Syntax
DATE_TRUNC('field', source)
Semantics
field is a string constant that selects the precision to which truncate the input value. Valid values for field are:
century day decade hour microseconds millennium |
milliseconds minute month second week year |
source is a value expression of type TIMESTAMP or INTERVAL. (Values of type DATE and TIME are cast automatically, to TIMESTAMP or INTERVAL respectively.)
Examples
SELECT DATE_TRUNC('hour', TIMESTAMP '2001-02-16 20:38:40');
Result: 2001-02-16 20:00:00
SELECT DATE_TRUNC('year', TIMESTAMP '2001-02-16 20:38:40');
Result: 2001-01-01 00:00:00