Question

In an SQL query, which SQL keyword is used to implement a subquery?

a) GROUP BY
b) HAVING
c) ORDER BY
d) SELECT
e) SORT BY

Answer 1

The SQL keyword for implementing a subquery is 'SELECT'. Subqueries are used within another query to provide data for that main query, and they can be used in various parts of a SQL statement such as the WHERE and HAVING clauses.

Step-by-step explanation:

In an SQL query, the keyword used to implement a subquery is d) SELECT. A subquery, also known as an inner query or nested query, is a query within another SQL query and is enclosed in parentheses. Its purpose is to return data that will be used in the main query as a condition to further refine the data to be retrieved. Subqueries can be used in various parts of a SQL statement, including the WHERE clause, the HAVING clause, and the FROM clause.

To illustrate, consider a scenario where you want to find employees who have a salary higher than the average salary of all employees. You could use a subquery as follows:

SELECT employee_id, name, salary
FROM employees
WHERE salary > (SELECT AVG(salary) FROM employees)

In this example, the subquery calculates the average salary and the outer query selects only those employees whose salary exceeds this average.