SQL Where to filter on Nested query

I have a query that looks like this:

Insert Into tblX (a,b,c)
Select x as a, y as b
   (select top 1 whatever from tblZ as z where z.aID  = y.aID order by z.s desc) as c
from tblY as y
where y.foo = 'bar'
AND c <> NULL

The problem is that last line. It tells me that c is an invalid column name. using y.c as well, to the same result. I need to not inset rows where that giant inner query is null, becau开发者_开发百科se tblX cannot accept nulls there. I feel like I should be able to filter on that column, but I can't quite get the syntax right.

---

You will probably need to double-nest this query.

Also, depends on your DBMS, but you should be checking C IS NOT NULL

You are using two tables without a join. If you tell us what you are trying to achieve, we can help better.

---

What ended up working is double nesting the query.

Insert Into tblX (a,b,c)
  Select a,b,c from
    (select x as a,
           y as b,
     (select top 1 whatever from tblZ as z where z.aID  = y.aID order by z.s desc) as c
      from tblY as y where y.foo = 'bar') as foobar
  Where c IS NOT NULL