为什么rs = stmt.executeUpdate();会报错

<%
            //取商品信息值            
            PreparedStatement stmt=null;            
            ResultSet rs=null;
            
            String sql="insert into order select * from cart;";                        
            stmt=conn.prepareStatement(sql);
            rs = stmt.executeUpdate();
            //String name = null;
            sql = "select * from order;";
            stmt = conn.prepareStatement(sql);
            rs = stmt.executeQuery();
            String id,name,price,count,IMG;                
            int num=0;
            
        %>

报啥错啊