How do I add where condition?

Question

I want to add a condition according to the returned result

Answer 1

You can't reuse an alias defined in the SELECT clause in the FROM clause of the scope. You need to either repeat the expression, or use a subquery or CTE.

select dayofweek_iso(timestamp(mycol)) as mynewcol 
from mytable
where dayofweek_iso(timestamp(mycol)) = 1

Or:

select *
from (
    select dayofweek_iso(timestamp(mycol)) as mynewcol 
    from mytable
) t
where mynewcol = 1