SQL

mysql if

SELECT user_display_image AS user_image,
       user_display_name AS user_name,
       invitee_phone,
       (CASE WHEN invitee_status = 1 THEN "attending"
             WHEN invitee_status = 2 THEN "unsure"
             WHEN invitee_status = 3 THEN "declined"
             WHEN invitee_status = 0 THEN "notreviwed"
       END) AS invitee_status
  FROM your_table

mysql if statement

-- PL/SQL
BEGIN
    IF my_val = 1 THEN [...]
    ELSE [...]
    END IF;
END;
-- In a query
SELECT CASE WHEN my_col = 1 THEN 'Ok' ELSE 'Ko' END AS my_result;

mysql if statement in where clause

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

MySQL if condition

The if accept one condition, if this condition is true then the true_value will occur 
else the false_value will occur.
IF(condition, true_value, false_value)
Tips : can be to update some data