Google Data Analytics Professional Certification Practice Test

Which of the following best describes a subquery?

1. A standalone SQL command

2. A query that provides a dataset for further analysis

3. A SQL query nested within a larger query

4. A table created for permanent storage

The correct answer is: A SQL query nested within a larger query

A subquery is best described as a SQL query nested within a larger query. This means that the subquery operates as a component of the main query and can be utilized to perform operations like filtering data or calculating values that the main query depends on. The subquery is executed first, allowing its results to be used by the main query, facilitating more complex data retrieval and analysis. For example, in a scenario where you want to select all employees who earn more than the average salary, the subquery would first calculate the average salary, and then the main query would use that result to filter the employees. This nesting allows for more organized and efficient query writing, enabling sophisticated data manipulation with less redundancy. In contrast, a standalone SQL command refers to a complete and independent SQL statement that operates on its own without being part of another query. This does not capture the essence of a subquery's function. A query that provides a dataset for further analysis could refer to various types of queries, but it lacks the specific characteristic of being part of another query structure. Likewise, a table created for permanent storage describes a database schema element rather than the functional aspect of queries in SQL, which further sets it apart from what defines a subquery.