WITH provides a way to write auxiliary statements for use in a larger query.

 These statements, which are often referred to as Common Table Expressions or CTEs, can be thought of as defining temporary tables that exist just for one query.

 Each auxiliary statement in a WITH clause can be a SELECT, INSERT, UPDATE, or DELETE; and the WITH clause itself is attached to a primary statement that can also be a SELECT, INSERT, UPDATE, or DELETE.

https://www.codejava.net/frameworks/spring-boot/connect-to-postgresql-database-examples