SQL QUERY

Question

What is the answer of below query and please give detailed answer how exists work as i think it only check row in inner query exist or not?

Answer 1

0,3 and 1 are the number of tuples for Q1, Q2 and Q3 repsectively.

First, the outer query executes and then for each tuple of the output of the outer query, Inner query executes, if the inner query results in atleast one tuple, then EXISTS returns TRUE, if exists returns TRUE, then corresponding tuple of the outer query's ouptut is printed or listed.

And NOT EXISTS is opposite of TRUE.

Please correct me if i am wrong.

Comments

Is below tupples are as output for

0  3 1

For 0 nothing

For 3

          T1A T2B

            a  aa

            b  bb

            c  cc

           

        T1A T2B

            b  bb

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Yes ..