How to create an alphanumeric sequence like AAAA0000 and so on

I want to create an alphanumeric sequence like this: AAAA0000 AAAA0001 AAAA0002 AAAA0003 . . . AAAA9999 AAAB0000 AAAB0001 . . . ZZZZ9999 I have created this store procedure to do that but its too slow: CREATE OR REPLACE FUNCTION public.fn_batch_seq() RETURNS text LANGUAGE plpgsql AS $body$ DECLARE v_sequence TEXT := ''; v_next_sequence TEXT := ''; v_existing_id BIGINT := 0; BEGIN /* * VARCHAR BATCH SEQUENCE FOR SIMCARDS */ SELECT "sequence" FROM batch_sequence WHERE id = 1 INTO v_sequence; IF v_sequence = '' THEN RAISE NOTICE 'Error - No existe ningun registro en batch_sequence almacenado'; RETURN -500; END IF; SELECT perl_increment(v_sequence) INTO v_next_sequence; IF v_next_sequence = '' THEN RAISE NOTICE 'Error - La siguiente secuencia generada devolvio null o vacio'; RETURN -500; END IF; UPDATE batch_sequence SET "sequence" = v_next_sequence WHERE id = 1; RETURN v_next_sequence; EXCEPTION WHEN OTHERS THEN /* * Other errors */ RAISE NOTICE 'Error General - Posibles causas: No existe la tabla batch_sequence o no existe ningun registro en la misma'; RETURN -500; END; $body$ VOLATILE COST 100; This procedure uses a table to store the sequence: CREATE TABLE batch_sequence ( id serial NOT NULL, sequence text DEFAULT 'AAAA0000'::text NOT NULL ); -- Column id is associated with sequence public.batch_sequence_id_seq ALTER TABLE batch_sequence ADD CONSTRAINT batch_sequence_pk PRIMARY KEY (id); And for increment the sequence I use a perl procedure: CREATE OR REPLACE FUNCTION public.perl_increment(text) RETURNS text LANGUAGE plperl AS $body$ my ($x) = @_; if (not defined $x) { return undef; } ++$x; $body$ VOLATILE COST 100; It works very slow with large amount of data, because it must be executed before inserting every single row. Is there another way to do that with or without Perl?