mysql if and code example

Example 1: mysql select else if

select id, 
    (
    CASE 
        WHEN qty_1 <= '23' THEN price
        WHEN '23' > qty_1 && qty_2 <= '23' THEN price_2
        WHEN '23' > qty_2 && qty_3 <= '23' THEN price_3
        WHEN '23' > qty_3 THEN price_4
        ELSE 1
    END) AS total
 from product;

Example 2: mysql if statement in where clause

SELECT  `id` ,  `naam` 
FROM  `klanten` 
WHERE IF(`email` != '', `email`, `email2`) LIKE  '%@domain.nl%'