What is a subquery?

A subquery is defined as a query nested within another query. This means that it is an SQL statement that is embedded inside another SQL statement, allowing for more complex data retrieval and manipulation. For instance, a subquery can be used in the WHERE clause to filter results based on an aggregation or condition derived from another query, making it a powerful tool for working with related data in databases.

The concept of a subquery enhances the capabilities of database queries by enabling layered queries, which can streamline the retrieval of data based on dynamic conditions rather than running multiple separate queries. This nested approach can optimize data processing and help achieve results that would be cumbersome with simpler queries.

Other options describe different aspects of queries but do not capture the specific nature of a subquery. A typical query might access data from one table, which is too narrow to define a subquery. A query that does not return results does not provide any meaningful information about the structure or purpose of a subquery. Lastly, a type of report used for data visualization is unrelated, as that pertains to the presentation of data rather than the method of querying it.