Sams Teach Yourself SQL in 10 Minutes, Second Edition

Performing Mathematical Calculations

Another frequent use for calculated fields is performing mathematical calculations on retrieved data. Let's take a look at an example. The Orders table contains all orders received, and the OrderItems table contains the individual items within each order. The following SQL statement retrieves all the items in order number 20008:

SELECT prod_id, quantity, item_price
FROM OrderItems
WHERE order_num = 20008;

prod_id       quantity       item_price
----------    -----------    ---------------------
RGAN01        5              4.9900
BR03          5              11.9900
BNBG01        10             3.4900
BNBG02        10             3.4900
BNBG03        10             3.4900

The item_price column contains the per unit price for each item in an order. To expand the item price (item price multiplied by quantity ordered), ...