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Aptitude | GATE CS 1998 | Question 54
Which of the following query transformations (i.e., replacing the l.h.s. expression by the r.h.s. expression) is incorrect? R1 and R2 are relations. C1, C2 are selection conditions and A1, A2 are attributes of R1.
a. σC1( σC2R1)) → σC2(σC1(R1))
b. σC1( πA1R1)) → πA1(σC1(R1))
c. σC1( R1 ∪ R2 ) → σC1(R1) ∪ σC1(R2)
d. πA1(σC1(R1)) → σC1 (πA1 (R1))
(A)
a
(B)
b
(C)
c
(D)
d
Answer
Please comment below if you find anything wrong in the above post
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