MadeEasy Subject Test: Databases - Sql

Question

Please explain how??

Comments

i also got same answer.

inner query always returns null value,so count value always 0.

So no tuple exists.It(R) prints values only inner query returns one or more values.

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But in explaination they were saying that although in inner query no tuple satisfies the condition but the output of count * will result one tuple.
I didn't get what they are saying. Are you confidant about the answer?

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counting null values is treated as 1.

This is the only aggregate function deals with null.

So outer query prints all tuples in its relation.

http://stackoverflow.com/questions/1271810/counting-null-and-non-null-values-in-a-single-query

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Thanks :) I almost forget these things.

Answer 1

Answer : (c) 3- Rows

It will return all the rows, as 0 value of count is cosidered to be the Existing value,so TRUE is returned.

• WHERE EXISTS tests for the existence of any records in a subquery.
• EXISTS returns true if the subquery returns one or more records.
• EXISTS is commonly used with correlated subqueries.