CREATE OR REPLACE  FUNCTION schematree.gray2 ( t text )
RETURNS text AS
$BODY$
DECLARE 
    a text;
    b text; 
    dsp text;
    f integer;
BEGIN   
    dsp  = substr(t,char_length(t),1) ;
    f  = 7; 
    CASE dsp
     WHEN '0','1','2','3','4','5','6','7','8','9' THEN
          a   = substr(t, 7-dsp::integer , dsp::integer );
          b   = substr(t, 7, char_length(t) - 7 ) ;    
             RETURN  (a||','||b);
     WHEN 'Y' THEN
        RETURN  ('Y');
     WHEN 'Z' THEN
        RETURN  ('Z');
     END CASE;
END
$BODY$
LANGUAGE plpgsql STRICT VOLATILE COST 100;
 
 
SELECT * from schematree.gray2('$221000010191') ;