所以应该使用外连接查询：left join on 或者right join on.

例如在工单管理部分绑定到gridview时使用的查询语句如下：

string sql = "select tb_list.*,c_khmc,StandardHour from tb_list left join tb_vehicle on tb_list.vID=tb_vehicle.vID left join tb_Client on tb_vehicle.c_khbh=tb_Client.c_khbh left join tb_Maintain on tb_list.MaintainID=tb_Maintain.MaintainID ";

            DataTable dt = new DataTable();

            SqlDataAdapter da = new SqlDataAdapter(sql, conn.con);

            da.Fill(dt);

            grdv.DataSource = dt;

            grdv.DataBind();