(a)
SELECT user_id FROM user_table WHERE user_name='bob';
SELECT cart_item, product_id FROM shopping_cart WHERE user_id=77;
SELECT product_name FROM products WHERE product_id=231;
SELECT product_name FROM products WHERE product_id=527;
SELECT product_name FROM products WHERE product_id=1099;

(b)
SELECT u.user_id, c.cart_item, p.product_id, p.product_name
     FROM user_table as u, shopping_cart as c, products as p
     WHERE u.user_name='bob'
        AND u.user_id=c.user_id
        AND c.product_id=p.product_id;

Example 2: Two different ways to get the same data. (a) With a lot of little queries; (b) with a single, more complex query.