Group query results by month and year in postgresql

Question

I can’t believe the accepted answer has so many upvotes — it’s a horrible method.

Here’s the correct way to do it, with date_trunc:

   SELECT date_trunc('month', txn_date) AS txn_month, sum(amount) as monthly_sum
     FROM yourtable
 GROUP BY txn_month

It’s bad practice but you might be forgiven if you use

 GROUP BY 1

in a very simple query.

You can also use

 GROUP BY date_trunc('month', txn_date)

if you don’t want to select the date.