Common Table Expression(CTEs) is a handy feature in PostgreSQL, it is a temporary result set that you can reference within another SELECT, INSERT, UPDATE, or DELETE statement. It provides a convenient way to manage the completed queries. CTEs are defined within the PostgreSQL statement using the WITH clause. It resolves many difficulties we face in the PostgreSQL query statement such as removes the complexity of sub-query, which executed multiple times, equally helpful in place of temporary tables.