IF statement in MySQL as an Event

Sorry that I'm completely clueless about this. But what I'm trying to do is this:

Under a table, I have two columns, group_1 and group_2. I want to run a daily event where if group_1 and group_2 have the same value 12, group_2 becomes empty.

This is the awful piece of code I have:

BEGIN
IF GROUP_1 = 12 AND GROUP_2 = 12 THEN
            UPDATE GROUP_2 SET GROUP_2 = ''
        END IF;
END

Any help would be appreciated :)

UPDATE 1:

Someone suggested using CASE function. This is what I came up with. Still no luck:

SELECT member_group_id, mgroup_others,
CASE
    WHEN member_group_id = 12 AND mgroup_others = 12
    THEN SET mgroup_others = ''
END
FROM core_members;