Getting the sum of several columns from two tables

Question

I want to get the sum of several columns from 2 different tables (these tables share the same structure).

If I only consider one table, I would write this kind of qu

Answer 1

You can union your tables before the group by (this is on Oracle, by the way):

SELECT t.month_ref, SUM(t.amount1), SUM(t.amount2)
  FROM (SELECT month_ref, amount1, amount2
          FROM T_FOO
         WHERE seller = XXX
         UNION ALL
        SELECT month_ref, amount1, amount2
          FROM T_BAR
         WHERE seller = XXX
         ) t
 GROUP BY t.month_ref

You may also union the tables with the seller field and filter by it later (in case you need more advanced logic):

 SELECT t.month_ref, SUM(t.amount1), SUM(t.amount2)
   FROM (SELECT month_ref, amount1, amount2, seller
           FROM T_FOO
          UNION ALL
         SELECT month_ref, amount1, amount2, seller
           FROM T_BAR) t
  where t.seller = XXX
  GROUP BY t.month_ref