plpgsql function

Hello.

I wrote a little stored function to simulate the EXTRACT(YEAR_MONTH ...)
from mySQL.

//---------------------------------
CREATE OR REPLACE FUNCTION "BiSCAT_combined".extractyearmonth(date
timestamp without time zone)
RETURNS character varying AS
$BODY$

DECLARE i INTEGER;

BEGIN
i := EXTRACT(MONTH FROM $1 ::timestamp);
if i > 9 THEN
RETURN EXTRACT(YEAR FROM $1 :: timestamp) || EXTRACT(MONTH FROM $1 ::
timestamp);
else
RETURN EXTRACT(YEAR FROM $1 ::timestamp) || 0 || EXTRACT(MONTH FROM
$1 :: timestamp);
end if;

END;
$BODY$
LANGUAGE 'plpgsql' IMMUTABLE STRICT;

//--------------------

One Method call requires 53ms.
I'm sure that this function is absolutely unoptimezed but I think
53ms is too long.

Are there any suggestions to improve the execution time of the function.

Best regards

Andi Kendlinger