Consider relational schema: Suppliers(sid, sname...), Parts(pid, pname...), Catalog(sid, pid, pcost). Query: (SELECT catalog.pid from Suppliers, Catalog WHERE Suppliers.sid = Catalog.sid) MINUS (SELECT catalog.pid from Suppliers, Catalog WHERE Suppliers.sid = Catalog.sid AND sname != 'Sachin').
- A. Pid of parts supplied by all except Sachin
- B. Pid of parts supplied only by Sachin
- C. Pid of parts available in catalog supplied by Sachin
- D. Pid of parts available in catalog supplied by all except Sachin
Answer: B. Pid of parts supplied only by Sachin
Explanation: Set A: All parts supplied by anyone. Set B: All parts supplied by anyone who is NOT Sachin. A - B = Parts supplied by (Anyone) AND NOT (Anyone who is NOT Sachin). This implies parts supplied ONLY by Sachin. If a part is supplied by Sachin and also by Rahul, it is in A. It is also in B (supplied by Rahul). So it is removed. Result contains parts supplied EXCLUSIVELY by Sachin.