Name  Qty
a      4
b      5
c      6

Name  Qty
a      7
b      8
c      9

Name  Qty
a      11

SELECT t.name,t.qty+s.qty
FROM tableA t
INNER JOIN tableB s on(t.name = s.name)

SELECT name,sum(qty) from(
    SELECT name,qty FROM TableA
    UNION ALL
    SELECT name,qty from TableB)
GROUP BY name