Date_trunc by month? Postgresql

Question

How would I get the date_trunc by month? Would it be like this?

SELECT date_trunc('month', l_date) month
    FROM this_table
    GROUP BY month

l_date is the column where I would pull the date from.

Answer 1

Yes, that should work just fine in Postgres. Have you tested it?

If your date is 2014-03-16 10:00:00am:

date_trunc('month', l_date) would give you 2014-03-01 00:00:00 (sets it to first day of truncated month)

date_part('month', l_date) would give you 03 which it looks like that is what you are looking for