Using GROUP BY with UNION
Using GROUP BY with UNION in a PostgreSQL query.
The syntax for using
GROUP BY in Postgres with a
UNION can be confusing at first and took me a few tries to get right.
SELECT id FROM table_one
SELECT id from table_two
GROUP BY table_one.id
SELECT * FROM
(SELECT id as id_1 FROM table_one
SELECT id as id_2 from table_two) subquery
GROUP BY subquery.id_1
As you can see, you will need to create a subquery, select each column from that subquery, and then you can group by in the parent query.