I use below code to verify that DB2 Express Edition does support OUT parameter. I create a simple DB2 stored procedure:
CREATE OR REPLACE PROCEDURE DB2PROC_DB2 (IN INPARAM CHAR(20), OUT OUTPARAM CHAR(80))
P1: BEGIN
DECLARE v_INPARAM CHAR(20);
SET v_INPARAM = INPARAM;
SET OUTPARAM = TRIM(v_INPARAM) || ' COBOL WORLD!!!';
END P1
I call above Stored Procedure, OUT parameter works perfectly: