//第一种
            SqlDataAdapter daStudent = new SqlDataAdapter(cmd);
            DataSet dsStudent = new DataSet();
            daStudent.Fill(dsStudent,"Student");
            dtStudent = dsStudent.Tables["Student"];
            //第二种
            SqlDataAdapter studentDa = new SqlDataAdapter();
            DataSet studentDs = new DataSet();
            DataTable studentTb = studentDs.Tables.Add("Student");
            studentDa.Fill(studentDs, "Student");