Question

I have a situation where I want to sum difference between two tables. problem is that a row can exist in the second table and then I want to insert it as new row.

Pseudo

SELECT T1.seller, T1.code, T1.amount - T2.amount

Look at the image for an explanation

LINK

Answer 1

 DECLARE @T1 TABLE(
    seller VARCHAR(10),
    code VARCHAR(3) NULL,
    amount MONEY
)

 DECLARE @T2 TABLE(
    seller VARCHAR(10),
    code VARCHAR(3) NULL,
    amount MONEY
)

INSERT INTO @T1 VALUES
('VL',NULL,1),
('VL','317',70005.6)

INSERT INTO @T2 VALUES
('VL',NULL,0.5),
('VL','500',4450)

SELECT seller,code,SUM(amount) [amount] FROM 
(
SELECT * FROM @T1
UNION ALL
SELECT seller,code,-amount as amount FROM @T2
) T
GROUP BY seller,code