Sum a column from a table and subtract it to a summed column in another table

Question

I have two tables TblInventory and TblWithdrawal. TblInventory has productID as well as TblWithdrawal.

Grouping by ProductID, how do I SUM the Quantity in TblInventory and SUM the Quantity in TblWithdrawal and then SUBTRACT it to one another so I can get the remaining or difference in Quantity of each ProductID?

This is what I came up with, but when I run the query, it asks me to input a parameter which is wrong because I want it to automatically go through the table and do the operations on each ProductID.

SELECT TblInventory.ProductID,
       SUM(TblInventroy.Quantity) - SUM(TblWithdrawals.Quantity) As [Remaining]
FROM TblInventory
  LEFT JOIN TblWithdrawals ON TblInventory.ProductID = TblWithdrawals.ProductID 
WHERE TblInventory.ProductID = TblWithdrawals.ProductID
GROUP BY TblInventory.ProductID

Thank you. I really need to solve this!

Answer 1

Don't user WHERE clause. And use INNER JOIN instead of LEFT JOIN

Answer 2

Use Sub queries,First write group sqls then join it as you want. Look following sql.

SELECT invent.ProductID, invent.invQty- withdrawl.withdrQty as Remaining
FROM ( SELECT ProductID,SUM(Quantity) as invQty
FROM TblInventory ) as invent
LEFT OUTER JOIN
( SELECT ProductID,SUM(Quantity) as withdrQty
FROM TblWithdrawals ) as withdrawl
ON invQty.ProductID=withdrawl.ProductID

Try This Best wishes