MONTH

Return the month number (1 through 12) from a date or timestamp expression:
MONTH(expression)
For example:
premdb=# select month(matchday), matchday from match where htid=2 and atid=60;
 month |      matchday       
-------+---------------------
     3 | 2010-03-06 00:00:00
(1 row)

premdb=# select month(date '2017-12-31') from sys.const;
 month 
-------
    12
(1 row)

premdb=# select month(timestamp '2017-11-30 15:30:10') from sys.const;
 month 
-------
    11
(1 row)

See also YEAR and DAY.