a simple way to sum a result from UNION in MySql

Question

I have a union of three tables (t1,t2,t3). Each rerun exactly the same number of records, first column is id, second amount:

1  10
2  20
3  20

1  30
2  3         


        

Answer 1

Not sure if MySQL uses common table expression but I would do this in postgres:

WITH total AS(
              SELECT id,amount AS amount FROM table_1 UNION ALL
              SELECT id,amount AS amount FROM table_2 UNION ALL
              SELECT id,amount AS amount FROM table_3
             )
SELECT id, sum(amount)
  FROM total

I think that should do the trick as well.