Question

I have 2 tables like this:

Stock Table
product_id bigint(20)
qty float

Sales Table
product_id bigint(20)
qty float

Sample Data
Stock Table
product_id—qty
1—10
2—11
3—20
4—50
1—10
3—10

Sales Table
product_id—qty
1—2
2—5
3—20
4—40
1—7

I want the following Output after running the Query
product_id—qty
1—11
2—6
3—10
4—10

Well, as spender ask I am trying to more clear the situation.

First of All, let’s think that I store
10 quantity of product 1
11 quantity of product 2
20 quantity of product 3
50 quantity of product 4
10 quantity of product 1 (now I have total 20 of product 1)
10 quantity of product 3 (now I have total 30 of product 3)

Secondly, let’s think that I sell
2 quantity of product 1
5 quantity of product 2
20 quantity of product 3
40 quantity of product 4
7 quantity of product 1 (now I have sold total 9 of product 1)

Thirdly, I want to know how much stock is now in my hand
11 quantity of product 1 (20-9 = 11)
6 quantity of product 2 (11-5 = 6)
10 quantity of product 3 (30-20 = 10)
10 quantity of product 4 (50-4 = 10)

My Question is: To find out this stock what is the Query?

Thanks in Advance for answering my question.

Answer 1

Chris’s answer is absolutely correct. But for the information I want to add this one which I found on NET.

SELECT tunion.product_id, (  
(IFNULL((SELECT SUM(s.qty) FROM stock s WHERE s.product_id=tunion.product_id),0))-  
(IFNULL((SELECT SUM(p.qty) FROM sales p WHERE p.product_id=tunion.product_id),0)))  
AS quantity   
FROM (SELECT DISTINCT s.product_id FROM stock s  
UNION ALL SELECT DISTINCT p.product_id FROM  sales p)  
AS tunion GROUP BY tunion.product_id