1Z0-071 Using Subqueries

Question 1

What is a subquery in Oracle SQL?

Accepted Answer

A SELECT statement nested inside another SQL statement

Answer

A subquery is a SELECT statement embedded within another SQL statement such as a SELECT, INSERT, UPDATE, or DELETE.

Question 2

Where can a single-row subquery be used in a SELECT statement?

Accepted Answer

In the WHERE, HAVING, and SELECT clauses

Answer

Single-row subqueries can appear in the WHERE, HAVING, and SELECT clauses of the outer query.

Question 3

Which comparison operator is INVALID when used with a multi-row subquery?

Accepted Answer

=

Answer

The = operator expects a single value; using it with a multi-row subquery causes an ORA-01427 error.

Question 4

What does the EXISTS operator check in a subquery?

Accepted Answer

Whether the subquery returns at least one row

Answer

EXISTS returns TRUE if the subquery produces at least one row, regardless of column values.

Question 5

A subquery that returns more than one column is called a:

Accepted Answer

Multiple-column subquery

Answer

A multiple-column subquery returns more than one column and is typically used in pairwise comparisons.

1Z0-071 - Oracle Database SQL Certified Associate Practice Test