Nested CASE statements in MySQL

Question

My first time working with CASE Logic in SQL statements. Everything works if I remove the CASE statements, so the SQL is valid without it.

I need to calculate the total item price based on a couple of things.

If "Sales Price" is active AND "Option Upcharge" has a value, the total is: Qty * (Sales Price + Option Upcharge)

If "Sales Price is inactive AND "Option Upcharge" has a value, the total is: Qty * (Price + Option Upcharge)

If "Sales Price" is active AND "Option Upcharge" has NO value, the total is: Qty * Sales Price

If "Sales Price is inactive AND "Option Upcharge" has NO value, the total is: Qty * Price

If no Option was added, the value for tblproduct_options.option_upcharge is NULL in the output.

Thanks for the help.

Brett

Here is my SQL:

SELECT 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,
CASE
WHEN (tblproducts.product_sale_price_status = 'Y')
    CASE
    WHEN (tblproduct_options.option_upcharge IS NOT NULL)
        THEN (tblshopping_cart.product_qty * (tblproducts.product_sale_price + tblproduct_options.option_upcharge)) 
        ELSE (tblshopping_cart.product_qty * tblproducts.product_sale_price)    
    END
ELSE
    CASE
    WHEN (tblproduct_options.option_upchage IS NOT NULL)
        THEN (tblshopping_cart.product_qty * (tblproducts.product_price + tblproduct_options.option_upcharge))
        ELSE (tblshopping_cart.product_qty * tblproducts.product_price)
    END
END AS product_total
FROM tblshopping_cart
INNER JOIN tblproducts ON tblshopping_cart.product_id = tblproducts.product_id
LEFT JOIN tblproduct_options ON tblshopping_cart.product_option = tblproduct_options.option_product_id
ORDER BY tblshopping_cart.product_qty ASC

It fails with with message:

CASE
    WHEN (tblproduct_options.option_upcharge IS NOT NULL)
        THEN (tblshopping_' at line 4

Answer 1

You are missing a THEN in your first CASE Statement. (sorry I had to add table aliases)

SELECT sc.session_id
    , sc.product_id
    , sc.product_qty
    , sc.product_option
    , p.product_title
    , p.product_price
    , p.product_sale_price_status
    , p.product_sale_price
    , po.option_text
    , po.option_upcharge
    , CASE
        WHEN (p.product_sale_price_status = 'Y')
        THEN <-- add this
            CASE
            WHEN (po.option_upcharge IS NOT NULL)
                THEN (sc.product_qty * (p.product_sale_price + po.option_upcharge)) 
                ELSE (sc.product_qty * p.product_sale_price)    
            END
        ELSE
            CASE
            WHEN (po.option_upchage IS NOT NULL)
                THEN (sc.product_qty * (p.product_price + po.option_upcharge))
                ELSE (sc.product_qty * p.product_price)
            END
        END AS product_total
FROM tblshopping_cart sc
INNER JOIN tblproducts p
    ON sc.product_id = p.product_id
LEFT JOIN tblproduct_options po
    ON sc.product_option = po.option_product_id
ORDER BY sc.product_qty ASC