What defines a subquery in SQL?

What defines a subquery in SQL?

• A. A SELECT statement embedded inside another SELECT statement.
• B. A join between two tables.
• C. A SELECT statement that uses only aggregate functions.
• D. A query that runs after the outer query finishes.

Answer: (A)

Subqueries are SELECT statements that are written inside another SQL statement. They’re placed in parentheses and used to provide values or a temporary result to the outer query, often in places like the WHERE clause or as a derived table in the FROM clause. For example, using an inner query to fetch a list of department IDs and then selecting employees whose department_id matches that list shows how the inner query feeds the outer one. This nests the logic rather than joining two tables side by side. It’s not limited to aggregates—the inner query can be simple or include aggregates—and it doesn’t run after the outer query finishes; the inner query is evaluated as part of the outer query, and a correlated subquery may run once per outer row.

Subqueries are SELECT statements that are written inside another SQL statement. They’re placed in parentheses and used to provide values or a temporary result to the outer query, often in places like the WHERE clause or as a derived table in the FROM clause. For example, using an inner query to fetch a list of department IDs and then selecting employees whose department_id matches that list shows how the inner query feeds the outer one. This nests the logic rather than joining two tables side by side. It’s not limited to aggregates—the inner query can be simple or include aggregates—and it doesn’t run after the outer query finishes; the inner query is evaluated as part of the outer query, and a correlated subquery may run once per outer row.