Question

What is the purpose of the 'exists' keyword in SQL?

1) To search for the presence of a single row meeting the stated criteria
2) To search for all occurrences of a row meeting the stated criteria
3) To search for rows that are not correlated
4) To search for rows that are correlated

Answer 1

The 'exists' keyword in SQL is used to check if a subquery returns at least one row that meets the specified criteria, essentially confirming the presence of a single row without retrieving data.

Step-by-step explanation:

The purpose of the 'exists' keyword in SQL is to search for the presence of a single row meeting the stated criteria. Specifically, it's used in a subquery to test if the subquery returns any rows. Rather than retrieving any data, it simply checks for existence. If the subquery returns at least one row, the EXISTS condition will evaluate to true, and if the subquery returns no rows, it will evaluate to false. This is particularly useful in correlated subqueries where the subquery's result is related to the outer query.