ShoppingCart

 1 CREATE TABLE [dbo].ShoppingCart
 2 (
 3 CartID INT IDENTITY(1,1) NOT NULL PRIMARY KEY,
 4 UserID INT NOT NULL,
 5 ProductID INT NOT NULL,
 6 Quantity INT NOT NULL
 7 )
 8 GO
 9 
10 CREATE PROC AddToShoppingCart
11 (
12     @UserID INT,
13     @ProductID INT
14 )
15 AS
16     DECLARE @ProductName VARCHAR(100),@UnitPrice MONEY
17     IF EXISTS(SELECT * FROM ShoppingCart WHERE ProductID = @ProductID AND UserID = @UserID)
18         BEGIN
19             UPDATE
20                 ShoppingCart
21             SET
22                 Quantity = Quantity + 1 
23             WHERE
24                 ProductID = @ProductID
25             AND
26                 UserID = @UserID
27         END
28     ELSE
29         BEGIN
30             SELECT
31                 @ProductName = ProductName,@UnitPrice = UnitPrice
32             FROM
33                 Product
34             WHERE
35                 ProductID = @ProductID
36     
37             INSERT INTO ShoppingCart(UserID,ProductID,Quantity) VALUES(@UserID,@ProductID,1)
38         END
39 GO