Question

In MySQL I have two tables:

Table MC:
----------------
|TransNo | Qty |
|--------|-----|
|  xxx1  |  4  | 
|  xxx3  |  3  |

and

Table Amex:
----------------
|TransNo  | Qty |
|---------|-----|
|  xxx1   |  2  |
|  xxx5   |  1  | 

I need to sum the Qty column from table MC (eq. 7) and table Amex (eq. 3) and have result as Total Qty.

When I do

SELECT (SUM(amex.Qty) + SUM(mc.Qty)) as total_qty from amex, mc

I get the cartesian product (20), but the correct answer I need is 10. How do I need to change this query to get the correct result?

Answer 1

SELECT SUM(t.Qty) AS total_qty
    FROM (SELECT Qty FROM MC
          UNION ALL
          SELECT Qty FROM Amex) t