DBMS query

Question

Consider the relationP(A,B,C),Q(C,D,E),R(E,F) having tuples 200, 300 and 100 respectively. The number of tuples in relation P join Q join R are ______.

Comments

you made 300 based on Primary key,rt? And primary keys gives the minimum no. of tuples.

I have done based on foreign key, which gives maximum value. So, my answer should give maximum number of tuples.rt?

Then why here just reverse answer?

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hahaha. : )

Check my  comment again ... I too have considered FK ... and used same logic as yours, But the difference is I have done first (Q join P) and you have done (P join Q), even then ans should be same because join is commutative.

But I have assumed different PK and FK ...

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hm, rt.

Conclusion : question is incomplete :P

Answer 1

IF question is asked for maximum number of tuples  and key constraintes can be imagined then the solution is as follows .
P and Q is related by C
Q and R is related by E =>  min (300,100) = 100
P and ( Qand R ) => min(200,100) = 100
Only 100 rows will be outputed .

Note : Natural Join Return min of two coloums if refertial integrity contraints holds good.
Given Question is ambigous without proper details

Reference : https://gateoverflow.in/2344/gate2010_43

Comments

This reference will not follow this question

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Yes, Question seems incomplete.

Either question should ask us to find  maximum/min touple or it should provide some info about commont elements between relations (like- CK, FK)..