UGC-NET | UGC NET CS 2016 Aug – II | Question 20

Consider a database table R with attributes A and B. Which of the following SQL queries is illegal ?
(A) SELECT A FROM R;
(B) SELECT A, COUNT(*) FROM R;
(C) SELECT A, COUNT(*) FROM R GROUP BY A;
(D) SELECT A, B, COUNT(*) FROM R GROUP BY A, B;

Answer: (B)
Explanation: SELECT A FROM R; legal query
SELECT A, COUNT(*) FROM R; Illegal query because we can’t SELECT A, COUNT(*) unless it is grouped by A.
SELECT A, COUNT(*) FROM R GROUP BY A; legal query
SELECT A, B, COUNT(*) FROM R GROUP BY A, B; legal query
So, option (B) is correct.

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