ISRO | ISRO CS 2017 | Question 13

Consider the following schema :

Sailors (sid, sname, rating, age)
Boats (bid, bname, colour)
Reserves (sid, bid, day)

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

ρ (Tempsids, (Ⲡ _{sid, bid} Reserves)/(Ⲡ_bid( σ _{bname ='Ganga'} Boats))),
Ⲡ _sname(Tempsids ⋈ 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 Gangaboat
(C) Names of sailors who have reserved at least one Gangaboat
(D) Names of sailors who have reserved at most one Ganga boat

Answer: (A)
Explanation: According to Division operator, Tempsids gives sid and bid of who have reserved all boats called Ganga

And Ⲡ _sname(Tempsids ⋈ Sailors) will return sname of sailors who have reserved all boats called Ganga

So, option (A) is correct.
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