一个mysql的存储过程，哪里有问题？

SQL code:

create procedure(in w varchar(20),out c int)
begin
set @sqlcount=concat('select count(*) into @c from scms_product where ',w);
prepare stm1 from @sqlcount;
execute stm1;
set c=@c;
set @sql=concat('select * from scms_product where ',w);
prepare stm2 from @sql;
execute stm2;
end


上面的存储过程在mysql里运行正常，要求在php里得到out变量c的值，php代码是这样的
PHP code:

$rs=$mysqli->query("call p5('cateid=5',@c)");
$res=$mysqli->query("select @c");
$row=$res->fetch_row();
echo $row[0];


运行的时候就会出现错误提示，Call to a member function fetch_row() on a non-object  如果我去掉存储过程中的
set @sql=concat('select * from scms_product where ',w);
prepare stm2 from @sql;
execute stm2;
这几行就正常了，请问我的php程序该怎么写？

---

create procedure(in w varchar(20),out c int)
begin
..


这个本身语法上就过不去。

建议你能贴出你实际问题的代码以便分析。

---

create procedure SP名字(in w varchar(20),out c int)
begin
set @sqlcount=concat('select count(*) into @c from scms_product where  ',w);
prepare stm1 from @sqlcount;
execute stm1;
set