Test: Nested Subqueries in SQL - Computer Science Engineering (CSE) MCQ

A subquery is a select-from-where expression that is nested within another query. Common uses for sub-queries are to perform tests for set membership, make set comparisons etc.

Nested Subqueries can be used for comparing two different sets. Set comparison is an important function of the nested sub-queries.

The all comparison checker is used to check “each and every” condition. The “each” and “every” comparison checkers do not exist in SQL.

A correlated sub-query is the one that uses the correlation name of an outer query.

SQL subqueries that can occur wherever a value is permitted provided the subquery gives only one tuple with a single attribute are called Scalar subqueries. Scalar Subqueries can be used in the SQL update statement when they are used under the set clause.

The in connective is used to test for the membership in a set, where the set is a collection of values given by the select clause.

The exists construct returns true if a given tuple is present in the subquery. The not exists construct gives true if a given tuple is not present in the subquery.

SQL allows the use of Subqueries inside the from clause. The subquery used in the from clause must have in its result the attributes that are specified in the select clause.

The unique construct returns true if the argument in the sub-query is void of duplicates. The not null construct avoids the specification of null values into the attribute.

The query gives the studentID with the maximum marks because the max(marks) aggregation gives the maximum of the marks.