Using group by and having clause

Question

Using the following schema:

Supplier (sid, name, status, city)
Part (pid, name, color, weight, city)
Project (jid, name, city)
Supplies (sid, pid, jid**, qua         


        

Answer 1

What type of sql database are using (MSSQL, Oracle etc)? I believe what you have written is correct.

You could also write the first query like this:

SELECT s.sid, s.name
FROM Supplier s
WHERE (SELECT COUNT(DISTINCT pr.jid)
       FROM Supplies su, Projects pr
       WHERE su.sid = s.sid 
           AND pr.jid = su.jid) >= 2

It's a little more readable, and less mind-bending than trying to do it with GROUP BY. Performance may differ though.