PostgreSQL/Store Procedure Function/Function Call

Call function in select statement

postgres=# CREATE FUNCTION "test" (integer) RETURNS integer AS "
postgres"#
postgres"#  DECLARE
postgres"#   variable ALIAS FOR $1;
postgres"#  BEGIN
postgres"#   return variable * 2;
postgres"#  END;
postgres"#  " LANGUAGE "plpgsql";
CREATE FUNCTION
postgres=#
postgres=# select test(1);
 test
------
    2
(1 row)
postgres=#
postgres=# drop function test(integer);
DROP FUNCTION
postgres=#
postgres=#