Question

I have two tables below.

Item Table

This Item Table contains ItemId and Total Quantity

ItemID   TotalItems     

 1        10

 2        10

 3        10

 4        10  

OrderHistory

Table This Order history table contains ItemId and OrderId

orderId    ItemID

 11          1

 12          1

 13          2

 14          2

 15          3

I want to get result which contains ItemID and total Items Used for example for Item Id 1 , there are two order in orderhistory so I want result like below

Remaining Items( Formula : Total Items from ItemTable – count of Same ItemId from Orderhistory table)

Final output :

ItemId Remaining Items

1    8

2    8

3    9

4    10

so How to write SQL Query for that.

Answer 1

Something like this?

SELECT i.ItemID, i.TotalItems - COUNT(h.ItemID) AS RemainingItems
FROM ItemTable i
    LEFT JOIN OrderHistory h
        ON i.ItemId = h.ItemId
GROUP BY i.ItemId, i.TotalItems