Example of WITH common table expression in PostreSQL

pg_with.sql

-- DOCUMENTATION: http://www.postgresql.org/docs/9.3/static/queries-with.html

/*
  WITH - defines auxilary stetments for larger query. Also called as 'Common Table Expressions' (CTE).
         It can create temporary tables just for one query.
         It is a basic CRUD statement atatched to another CRUD query.
*/

-- SYNTAX:

  WITH [RECURSIVE]  cte_name[(*arguments)]         AS ( /*     sql query     */ ),
                    another_cte_name[(*arguments)] AS ( /* another sql query */ )
                 
/*
  RECURSIVE modifier allows to call CTE itself what is not possible in 'regular' SQL.
  It actually behaves like iteration with passing arguments its own input.

  What is worth to mention is that one CTE can use other CTE already defined before it.
*/