drop procedure if exists proc_addNum;
 create procedure proc_addNum (in x int,in y int,out sum int)
 BEGIN
 SET sum= x + y;
 end

 call proc_addNum(2,3,@sum);
select @sum;

 drop procedure if exists proc_addNum;
 create procedure proc_addNum (in x int,in y int)
 BEGIN
 DECLARE sum int;
 SET sum= x + y;
 SELECT sum;
 end

 call proc_addNum(2,3);