MySQL UPDATE using IF condition

Question

I'm not even sure if this is possible but I'm trying to do different UPDATE if a certain condition is met.

user [id, start_date(NOT NULL), end_date(NULL), reason(NULL), .....]

user_roles [id, role_id, user_id, start_date(NOT NULL), end_date(NULL)]

What I have right now is this but this only works if a role exists for the user and it's end_date is NULL:

UPDATE user p 
JOIN user_roles ur ON p.id = ur.user_id 
SET ur.end_date = NOW()
   , p.end_date = NOW()
   , p.reason = "Retired" 
WHERE p.id = 5 
AND ur.end_date IS NULL

I was thinking of doing something like this:

IF EXISTS (SELECT id FROM user_roles 
WHERE user_id = 5 AND end_date IS NULL)
THEN 
    UPDATE user p 
    JOIN user_roles ur ON p.id = ur.user_id 
    SET ur.end_date = NOW()
        , p.end_date = NOW()
        , p.reason = "Retired" 
    WHERE p.id = 5 AND ur.end_date IS NULL 
ELSE 
    UPDATE user 
    SET end_date = NOW()
        , reason = "Retired" 
    WHERE id = 5 
END IF

Answer 1

Since the only difference is whether you are setting ur.end_Date to either the current Date or setting it to it's existing date could you not just use the following:

UPDATE user p
JOIN user_roles ur ON p.id = ur.user_id
SET ur.end_date = IF (ur.end_date IS NULL, NOW(), ur.end_date), p.end_date = NOW(), p.reason = "Retired" WHERE p.id = 5