Question

I have three tables linked each other.

mysql> select * from tablea;
+----+--------+
| id | name   |
+----+--------+
|  1 | Item 1 |
|  2 | Item 2 |
+----+--------+
2 rows in set (0.00 sec)

mysql> select * from tableb;
+----+------+----------+
| id | Aid  | name     |
+----+------+----------+
|  1 |    1 | B Item 1 |
|  2 |    2 | B Item 2 |
|  3 |    1 | B Item 3 |
+----+------+----------+
3 rows in set (0.00 sec)

mysql> select * from tablec;
+----+------+----------+-------+
| id | Bid  | name     | value |
+----+------+----------+-------+
|  1 |    1 | C Item 1 |    10 |
|  2 |    2 | C Item 2 |    20 |
|  3 |    1 | C Item 3 |    15 |
|  4 |    2 | C Item 4 |     5 |
|  5 |    3 | C Item 5 |    12 |
+----+------+----------+-------+
5 rows in set (0.00 sec)

TableA is linked to TableB with Aid, TableC is linked with TableB with Bid.

What I want is the id of tableA and the sum of values of all the TableC items comes under it.

The result set I expect for the above example is

+-----------+--------+
| tablea.id | sum    |
+-----------+--------+
|         1 |     37 |
|         2 |     25 |
+-----------+--------+

Answer 1

SELECT  a.ID, SUM(c.value) totalValue
FROM    tablea a
        INNER JOIN tableb b
            On a.ID = b.AID
        INNER JOIN tablec c
            ON b.ID = c.BID
GROUP BY a.ID

if there’s a possibility that ID from tableA doesn’t exist on other tables and you also want to show their result, use LEFT JOIN instead

SELECT  a.ID, COALESCE(SUM(c.value), 0) totalValue
FROM    tablea a
        LEFT JOIN tableb b
            On a.ID = b.AID
        LEFT JOIN tablec c
            ON b.ID = c.BID
GROUP BY a.ID

• SQLFiddle Demo for both queries