Question

I have two tables:
1. Master

| ID  |  Name  | Amount |
|-----|--------|--------|
| 1   |   a    | 5000   |
| 2   |   b    | 10000  |
| 3   |   c    | 5000   |
| 4   |   d    | 8000   |

2. Detail

| ID  |MasterID|  PID  |  Qty |
|-----|--------|-------|------|
| 1   |   1    |   1   |  10  |
| 2   |   1    |   2   |  20  |
| 3   |   2    |   2   |  60  |
| 4   |   2    |   3   |  10  |
| 5   |   3    |   4   |  100 |
| 6   |   4    |   1   |  20  |
| 7   |   4    |   3   |  40  |

I want to select sum(Amount) from Master which joins to Deatil where Detail.PID in (1,2,3)

So I execute the following query:

SELECT SUM(Amount) FROM Master M INNER JOIN Detail D ON M.ID = D.MasterID WHERE D.PID IN (1,2,3)

Result should be 20000. But I am getting 40000
See this fiddle. Any suggestion?

Answer 1

You are getting exactly double the amount because the detail table has two occurences for each of the PIDs in the WHERE clause.

See demo

Use

SELECT SUM(Amount) 
FROM Master M 
WHERE M.ID IN (
  SELECT DISTINCT MasterID
  FROM DETAIL
  WHERE PID IN (1,2,3) )