Self-join of a subquery

Question

I was wondering, is it possible to join the result of a query with itself, using PostgreSQL?

Answer 1

Do you mean, the result of a query on a table, to that same table. If so, then Yes, it's possible... e.g.

--Bit of a contrived example but...
SELECT * 
FROM Table
INNER JOIN
(
    SELECT 
          UserID, Max(Login) as LastLogin
    FROM
          Table
    WHERE 
          UserGroup = 'SomeGroup'
    GROUP BY
          UserID

) foo
ON Table.UserID = Foo.UserID AND Table.Login = Foo.LastLogin