1. The relation R(a,b) may have duplicate tuples. Which of the following queries

Question

1.   The relation R(a,b) may have duplicate tuples. Which of the following queries has a result that is guaranteed not to have duplicates, regardless of what tuples R contains? a) SELECT a, b FROM R GROUP BY a, b b) SELECT COUNT(a) FROM R GROUP BY b c) SELECT b FROM R WHERE b <> ANY (SELECT b FROM R) d) SELECT b FROM R WHERE b NOT IN (SELECT a FROM R) 1.   The relation R(a,b) may have duplicate tuples. Which of the following queries has a result that is guaranteed not to have duplicates, regardless of what tuples R contains?

Explanation / Answer

Answer : Both a) and d)

a) SELECT a, b FROM R GROUP BY a, b

d) SELECT b FROM R WHERE b NOT IN (SELECT a FROM R)

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