What I am trying to do here is I would like to parse
UNION ALL SELECT * from step_2 when there is value in variable
Step_2. Otherwise, it should only parse
select * from step_1. However the value of variable
Step_2 is not meaningful in my query. Therefore, I would like to comment it, making it not a functional code. Then it shows the error. Is this function supported in metabase? Or did I make any mistake?