date_part() is a system function for retrieving elements of a date or timestamp, similar to extract() .

date_part() was added in PostgreSQL 6.1 .

Usage

date_part(field text, source date) → double precision
date_part(field text, source interval) → double precision
date_part(field text, source timestamp) → double precision
date_part(field text, source timestamp with time zone) → double precision

date_part() does essentially the same thing as the SQL-standard extract() function, and was originally intended to provide Ingres compatibility. From PostgreSQL 14 it is recommended to use extract() , as that function now returns numeric , whereas the double precision value returned by date_part() and extract() (prior to PostgreSQL 14 ) can result in a loss of precision in certain cases.

Change history

In PostgreSQL 14 and later, the value returned by date_part() may not be identical to the one returned by extract() :

postgres=# WITH now AS (
  SELECT NOW() AS now
SELECT date_part('epoch', now.now), extract('epoch' FROM now.now)
  FROM now;
    date_part     |      extract      
------------------+-------------------
 1637913804.90921 | 1637913804.909210
(1 row)