[firebird-support] Return Result from Stored Procedure

[Kongthap Thammachat]

Dear All

I wanna create a stored procedure to return 'YYMM' of the current date 
for using as part of my document ID

This is my stored procedure PSQL so far

SET TERM ^ ;
CREATE PROCEDURE P_YEARMONTH_PREFIX
RETURNS (
     YYMM Char(4) )
AS
declare YY char(2);
   declare MM char(2);
BEGIN
   select substring(cast(extract(year from current_date) + 543 as 
char(4)) from 3 for 2)
   from rdb$database
   into :YY;

   select cast(extract(month from current_date) as char(2))
   from rdb$database
   into :MM;

   if (char_length(MM) = 1) then begin
     MM = '0' || MM;
   end

   result = YY || MM; -- why is this line get error
END^
SET TERM ; ^

I really don't know why is that line get error, please help, I really 
new to Firebird.

P.S. Firebird 2.5

Thanks.
Kongthap.