private static string connString = "Server = localhost\\SQLEXPRESS2014;DataBase = StudentManageDB;Uid = sa;Pwd = sa";
        
        /// <summary>
        /// 返回一个结果集
        /// </summary>
        /// <param name="sql"></param>
        /// <returns></returns>
        public static SqlDataReader GetReader(string sql)
        {
            SqlConnection conn = new SqlConnection(connString);
            SqlCommand command = new SqlCommand(sql, conn);
            try
            {
                conn.Open();
                return command.ExecuteReader(CommandBehavior.CloseConnection);
                //CommandBehavior.CloseConnection 该参数能够保证从外部关闭DataReader时，与之关联的Connection对象将随之关闭
            }
            catch (Exception ex)
            {
                throw ex;
            }
            finally
            {
                conn.Close();
            }
            //conn.Close();不能用此种方法关闭,关闭之后Read方法将不能使用
        }

        

static void Main(string[] args)
            {
                string sql = "select * from Students;select * from studentClass";
                SqlDataReader reader = SQLHelper.GetReader(sql);
                while (reader.Read())
                {
                    Console.WriteLine(reader["StudentId"] + "\t" + reader["StudentName"]);
                }
                if (reader.NextResult())
                {
                    while (reader.Read())
                    {
                        Console.WriteLine(reader["ClassId"] + "\t" + reader["ClassName"]);
                    }
                }
                reader.Close();//会同时关闭conn
            }