I'm trying to get a 'date' type that corresponds to the first day of the current month. Basically one of my tables stores a date, but I want it to always be the first of the month, so I'm trying to create a trigger that will get now() and then replace the day with a 1.
You can use the expression date_trunc('month', current_date)
. Demonstrated with a SELECT statement . . .
select date_trunc('month', current_date)
2013-08-01 00:00:00-04
To remove time, cast to date.
select cast(date_trunc('month', current_date) as date)
2013-08-01
If you're certain that column should always store only the first of a month, you should also use a CHECK constraint.
create table foo (
first_of_month date not null
check (extract (day from first_of_month) = 1)
);
insert into foo (first_of_month) values ('2015-01-01'); --Succeeds
insert into foo (first_of_month) values ('2015-01-02'); --Fails
ERROR: new row for relation "foo" violates check constraint "foo_first_of_month_check" DETAIL: Failing row contains (2015-01-02).