mysql is null condition using variables

where_null.sql

set @created_by = null; -- if the var is null, the comparison cant be with '='

select *
from users
where 
	IF(
		@created_by is null, users.created_by is null, -- both var and field are null
		@created_by = users.created_by -- normal comparison, when var is not null
	)
limit 1;