CREATE OR REPLACE FUNCTION reference_books.get_list_contragents(
    IN lim integer DEFAULT 0,
    IN offst integer DEFAULT 0)
  RETURNS TABLE(id integer) AS
$BODY$
BEGIN


 
  RETURN QUERY
  SELECT

  reference_books.contragents.id

  FROM reference_books.contragents
  WHERE reference_books.contragents.active = True
  ORDER BY reference_books.contragents.id ASC LIMIT lim OFFSET offst;

END;$BODY$
  LANGUAGE plpgsql VOLATILE
  COST 100
  ROWS 1000;

if <условие> then return query query1;
else return query query2;
end if;