> For the complete documentation index, see [llms.txt](https://vikram-bajaj.gitbook.io/cs-gy-6083-principles-of-database-systems/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://vikram-bajaj.gitbook.io/cs-gy-6083-principles-of-database-systems/main-1/sql/dml-commands/derived-relations.md).

# Derived Relations

SQL allows using an SQL subquery in the *from* clause.

Ex. Find the average instructors’ salaries of those departments where the average salary is greater than $42,000

```
select dept_name, avg_salary
from (select dept_name, avg (salary) as avg_salary
 from instructor
 group by dept_name)
where avg_salary > 42000;
```