ISRO-DEC2017-13

Question

Consider the following schema:

$\text{Sailors(sid,sname,rating,age)}$
$\text{Boats(bid,bname,colour)}$
$\text{Reserves(sid,bid,day)}$

Two boats can have the same name but the colour differentiates them.

The two relations

$\rho (Tempsids,(\pi _{sid,bid}\,Reserves)/(\pi_{bid}(\sigma_{bname='Ganga'}\,Boats ))),$
$\pi_{sname}(Tempside\Join Sailors)$

If $/$ is division operation, the above set of relations represents the query

• A. Names of sailors who have reserved all boats called Ganga.
• B. Names of sailors who have not reserved any Ganga boat.
• C. Names of sailors who have reserved at least one Ganga boat.
• D. Names of sailors who have reserved at most one Ganga boat.

Answer 1

Answer - a Name of sailor who have reserved all the boats called Ganga.
Division operator means ALL
Hence this will return all the boats who are named ganga.

Comments

ref: https://coronet.iicm.tugraz.at/Dbase1/scripts/rdbh06.htm

search for DIVISION on this page

Answer 2

 C should be answered Names of sailors who have reserved at least one Ganga boat.