I'm searching a way to insert this
SET GLOBAL group_concat_max_len=15000
WHERE id =1
UNION SELECT 1 , 2, IF( 1 >0, SET GLOBAL group_concat_max_len=15000,'B' )
You can't use a
SET statement inside an expression like you're doing, or even in a subquery. Execute the
SET in one statement by itself. The value you set will affect subsequent statements.
By the way, are you aware that
SET GLOBAL means the setting will affect all other MySQL connections on your server, and the setting will even persist after your current session is done, until you set it to something else? You might want to use
SET SESSION if you only want the value to affect your current session.