PostgreSQL, ticketing system to use numbered sequences

ticket_function.sql

-- returns and update the next value for a named ticket. 

CREATE OR REPLACE FUNCTION get_ticket(ticket_name varchar(50)) RETURNS INTEGER AS $$
DECLARE
 ticket INTEGER;                                                              --
BEGIN
    IF EXISTS (SELECT * FROM ticketing_ticket WHERE name = ticket_name FOR UPDATE) THEN
      UPDATE ticketing_ticket SET currval = currval + incval
        WHERE name = ticket_name RETURNING currval INTO ticket;                     --
      RETURN ticket;                                                          --
    ELSE
      INSERT INTO ticketing_ticket (name)
        VALUES(ticket_name) RETURNING currval INTO ticket;                       --
      RETURN ticket;                                                          --
    END IF;                                                                   --
END;                                                                          --
$$ LANGUAGE 'plpgsql';                                                        --

ticket_table.sql

-- Table: ticketing_ticket

CREATE TABLE ticketing_ticket
(
  id serial NOT NULL,
  name character varying(50) NOT NULL,
  currval integer NOT NULL DEFAULT 1,
  incval integer NOT NULL DEFAULT 1,
  CONSTRAINT ticketing_ticket_pkey PRIMARY KEY (id),
  CONSTRAINT ticketing_ticket_name_key UNIQUE (name)
)

ticket_test.sh

$ psql testdb < ticket_table.sql
$ psql testdb < ticket_function.sql
$ psql testdb
psql (9.1.7)
Type "help" for help.

testdb=> select * from get_ticket('ticket1');
 ticket 
--------
    1
(1 row)
testdb=> select * from get_ticket('ticket1');
 ticket 
--------
    2
(1 row)
testdb=> select * from get_ticket('ticket1');
 ticket 
--------
    3
(1 row)