Here is a subtle bug you can introduce into a query. Let’s pretend we are tracking coffee sales.
CREATE TABLE CoffeeSales
(
TransactionID int IDENTITY PRIMARY KEY,
Customer varchar(10) NOT NULL,
CoffeeType varchar(10) NOT NULL,
TransactionDate datetime NOT NULL,
Cost money NOT NULL
)
INSERT INTO CoffeeSales
VALUES('Joe', 'Decaf', '2004-04-17 07:30:00', 2.25)
INSERT INTO CoffeeSales
VALUES('Joe', 'Decaf', '2004-04-17 09:00:00', 3.25)
INSERT INTO CoffeeSales
VALUES('Joe', 'Mocha', '2004-04-17 17:00:00', 5.00)
INSERT INTO CoffeeSales
VALUES('Amy', 'Maple', '2004-04-17 15:00:00', 1.25)
INSERT INTO CoffeeSales
VALUES('Amy', 'Mocha', '2004-04-17 16:00:00', 4.75)
INSERT INTO CoffeeSales
VALUES('Amy', 'Mocha', '2004-04-17 17:00:00', 3.50)
Here is a query attempting to total up the sales for each...