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Nov2017 cs Q11

0. Given two relations R1(A, B) and R2(C, D), the result of following query
Select distinct A, B
from R1, R2
is guaranteed to be same as R1 provided one of the following condition is satisfied.

  • Option : B
  • Explanation : Select A,B From R1, R2 : In this query first we will take cartesian product of R1, R2 (R2 must be non empty)for this 0- R2 then select distinct A,B from cartesian product of R1, R2 (for A,B being distinct there should not any duplicate A,B). And Select A,B From R2 For this query A,B → No duplicate A,B. By combining condition for both query we will get the right condition. So, option (B) is correct.
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