很感谢你的答复！！

      返回SqlCommand格式的全部用户
        ******************************/
        #region###查询全部用户
        public SqlCommand Select_SqlCommand_Users()
        {
            try
            {
                using (DALUser o = new DALUser())
                {
                    SqlCommand myComm = new SqlCommand();
                    myComm = o.Select_SqlCommand_Users();
                    return myComm;
                }
            }
            catch (Exception e)
            {
                error = e.Message;
                return null;
            }
        }
        #endregion

    返回DataSet格式的全部用户
        ******************************/ 
        #region###查询全部用户
        public DataSet Select_AllUsers()
        {
            try
            {
                using (DALUser o = new DALUser())
                {
                    DataSet myDs = new DataSet();
                    myDs = o.Select_AllUsers();
                    return myDs;
                }
            }
            catch (Exception e)
            { 
                error = e.Message;
                return null;
            }
        }
        #endregion

Dataset我可以理解了，但SqlCommand还是有点不太理解，这是我找来的代码，你能再详细说一下吗？？麻烦你了！！

@Guo47470: 如果你想真正理解一个类，你应该看他继承哪个类，他有哪些方法，分别是干什么，而不是一知半解。我给你个链接，自己去看看吧。http://msdn.microsoft.com/zh-cn/library/system.data.sqlclient.sqlcommand.aspx