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Why option d is incorrect?

in Databases by Junior (639 points) | 65 views
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please type the question.... it is not clearly visible
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Last one is not right because it is joining those rows of R1 with R2 which are not having R = S.
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The answer given is correct.

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R1
P Q R
a b 1
c d 2
  R2
S T
1 e
2 f
3 g
R1 JOIN R2 WHERE R $\neq$ S
P Q R S T
a b 1 2 f
a b 1 3 g
c d 2 1 e
c d 2 3 g

Now if we SELECT R from this join we will still get {1,2}. So, it doesn't produce an empty relation.

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