postgresqlでfirst_day()関数

◆ first_day

DROP FUNCTION first_day( DATE );
CREATE FUNCTION first_day( DATE ) RETURNS DATE AS
'select cast(date_trunc(''month'', $1) as date)'
LANGUAGE 'sql';

◆ last_day

DROP FUNCTION last_day( DATE );
CREATE FUNCTION last_day( DATE ) RETURNS DATE AS
'select cast(date_trunc(''month'', $1) + interval ''1 month - 1 day'' as date)'
LANGUAGE 'sql';