What is a better way to write this SQL query?

Question

I have the following relations.

Suppliers( sid: integer, sname: string, address: string)
Parts(pid: integer, pname: string, color: string)
Catalog( sid: integer, pid: integer, cost: real)

The problem asks me to find the pnames of parts supplied by Acme Widget Suppliers and no one else. I wrote the following SQL statement; however I feel like this query is inefficient because of the repetition. I would like to know if there is a better way to write this query without repeating the selecting catalog part.

Select P.pname 
FROM Parts P 
WHERE P.pid IN (
    Select C.pid 
    FROM Catalog C 
    INNER JOIN Supplier S
    ON S.sid = C.sid 
    WHERE S.sname = "Acme Widget Suppliers" 
    AND C.pid NOT IN (
            SELECT C2.pid 
            FROM Catalog C2
            INNER JOIN Supplier S
            ON S.sid = C2.sid 
            WHERE S.sname <> "Acme Widget Suppliers"
        )
);

Answer 1

You are correct. The query you want to make can be greatly simplified. Try the following.

SELECT P.pname FROM Parts P, Suppliers S, Catalog C
WHERE C.pid = P.pid
AND C.sid = S.sid
AND S.sname == "Acme Widget Suppliers"

Answer 2

The correct query would be:

Select P.PName from Suppliers S1 
 join Catalog C1
  on S1.sid = C1.sid
  join parts P
   on P.pid = C1.pid
where  S1.sname = 'Acme Widget Suppliers'
 and not exists 
 ( select  1 from catalog C2 where C2.sid != C1.sid 
   and C2.pid = C1.pid)

The not exist is very efficient as it stops to search when it finds the first occurence.

SQL Fiddle