Gate2019 cs Q65

65Consider the following relations P(X,Y,Z), Q(X,Y,T) and R(Y,V).

P				Q				R
X	Y	Z		X	Y	T		Y	V
X1	Y1	Z1		X2	Y1	2		Y1	V1
X1	Y1	Z2		X1	Y2	5		Y3	V2
X2	Y2	Z2		X1	Y1	6		Y2	V3
X2	Y4	Z4		X3	Y3	1		Y2	V2

How many tuples will be returned by the following relational algebra query?
π_x(σ_{(P.Y = R.Y ∧ R.V = V2)}(P X R)) - π_x(σ_{(Q.Y = R.Y ∧ Q.T > 2}(Q X R))

Note – Numerical Type question

Option : B
Explanation :

π_x(σ_{(P.Y = R.Y ∧ R.V = V2)}(P X R)) ⇒
X
X2
.........(I)

Π_x (σ_{(Q.Y = R.Y ∧ Q.T > 2)} (Q × R)) ⇒
X
X1
.........(II)
I – II ⇒
X
X2
one record in result.

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