Calculating the SUM of (Quantity*Price) from 2 different tables

Question

I have two tables as follows

PRODUCT table

Id | Name | Price

And an ORDERITEM table

Id | Orde         


        

Answer 1

i think this - including null value = 0

 SELECT oi.id, 
         SUM(nvl(oi.quantity,0) * nvl(p.price,0)) AS total_qty 
    FROM ORDERITEM oi 
    JOIN PRODUCT p ON p.id = oi.productid 
   WHERE oi.orderid = @OrderId 
GROUP BY oi.id