Comment by MarkusWinand

Hi!

The first feature matrix you see is about checking of functional dependencies.

For example, PostgreSQL doesn't see the functional dependency between the columns ID and MA in the result of this query.

    SELECT id
         , max(a) ma
      FROM ...
     GROUP BY id

As a consequence, this query doesn't work, because the outer query refers to MA which is not in the GROUP BY clause of the outer query:

    SELECT COUNT(*) cnt
         , ma
      FROM (SELECT id
                 , max(a) ma
              FROM ...
             GROUP BY id) x
      GROUP BY id

Detecting these things makes life easier.