Problem with SELECT CASE WHEN THEN, 0 result Need an advice in  SELECT CASE WHEN THEN. In main, removed all unimportant function, usual select i.fav_id FROM users; i see original table:

fav_id
1
2
6
7


but i need change some id's for result will be: 

fav_id
1
3
6
8


i do:

SELECT i.fav_id = 
        CASE 
           WHEN 2 THEN 3
           WHEN 3 THEN 2
           WHEN 7 THEN 8
           WHEN 8 THEN 7
           ELSE i.fav_id
       END fav_id
FROM `favorites` AS i WHERE i.member = '123456'


i got:

fav_id
0
0
0
0


i'm new to select CASE selection but after searching alot manuals and examples, and did not fund how to solve my problem. thanx for your time !

used:
libmysql - mysqlnd 5.0.11-dev - 20120503 
PHP: 5.6.28-1+deb.sury.org~xenial+1
phpMyAdmin  4.5.4.1deb2ubuntu2
found solution, sorry, my mistake !

SELECT i.fav_id, 
        CASE 
           WHEN i.fav_id = 2 THEN 3
           WHEN i.fav_id = 3 THEN 2
           WHEN i.fav_id = 7 THEN 8
           WHEN i.fav_id = 8 THEN 7
           ELSE i.fav_id
       END fav_id
FROM `favorites` AS i WHERE i.member = '123456'