IF/THEN logic in SQL statements - sql

Question

Building a Shopping Cart app. Some products have options, some don't. I visitor can purchase a product either with or without the associate option if that product does have options.
I have the following JOIN statement to pull all the relative data for the shopping cart output:
SELECT tblshopping_cart.cart_id,
tblshopping_cart.session_id,
tblshopping_cart.product_id,
tblshopping_cart.product_qty,
tblshopping_cart.product_option,
tblproducts.product_title,
tblproducts.product_price,
tblproducts.product_sale_price_status,
tblproducts.product_sale_price,
tblproduct_options.option_text,
tblproduct_options.option_upcharge
FROM tblshopping_cart
INNER JOIN tblproducts ON tblshopping_cart.product_id = tblproducts.product_id
INNER JOIN tblproduct_options
ON tblshopping_cart.product_option = tblproduct_options.option_product_id
WHERE tblshopping_cart.session_id = '$session_id'
ORDER BY tblshopping_cart.product_qty ASC
It works if all the products in the cart all have associated tblshopping_cart.product_option's that exists in the tblproduct_options table. If a product doesn't have a valid option, it only returns those that do.
By default, any product added without an option gets added to the cart with the value of "0" for the product_option value. If the site user does choose an option, the option value gets added instead.
What I need to do is pull in the Options information (text and upcharge) IF that row has a valid option_product_id.

Answer 1

You should use a LEFT JOIN if you don't want to require your record set to have a relationship to product_option.
It would look like this:
LEFT JOIN tblproduct_options
ON tblshopping_cart.product_option = tblproduct_options.option_product_id

Answer 2

Instead of doing an INNER JOIN against tblproduct_options you should be doing a LEFT OUTER JOIN so that you get both products with and without an associated option.