/// <summary>
        /// 获取前20条学生数据及其班级信息
        /// </summary>
        /// <returns></returns>
        public List<Student> GetTop20Data()
        {
            List<Student> list = new List<Student>();
            string sql = "select top 20 MyStudent.*,MyClass.className from MyStudent inner join MyClass on MyStudent.FClassId=MyClass.classId";
            //Fid	FName	FAge	FGender	  FMath	  FEnglish	FClassId	FBirthday	className
            using (SqlDataReader reader=SqlHelper.ExecuteReader(sql, System.Data.CommandType.Text))
            {
                if (reader.HasRows)
                {
                    while (reader.Read())
                    {
                        Student s = new Student();
                        s.StudentId = reader.GetInt32(0);
                        s.Name = reader.GetString(1);
                        s.Age = reader.GetInt32(2);
                        s.Gender = reader.GetString(3);
                        s.MathScore = reader.IsDBNull(4) ? null : (int?)reader.GetInt32(4);
                        s.EnglishScore = reader.GetInt32(5);
                        s.Birthday = reader.GetDateTime(7);

                        StudentClass studentClass = new StudentClass();
                        studentClass.ClassId = reader.GetInt32(6);
                        studentClass.ClassName = reader.GetString(8);
                        s.Myclass = studentClass;

                        list.Add(s);
                    }
                }
            }

            return list;
        }
 /// <summary>
 /// 获得所有的班级信息
 /// </summary>
 /// <returns></returns>
 public List<StudentClass> GetClassMsg()
 {
     List<StudentClass> list = new List<StudentClass>();
     string sql = "select * from MyClass";
     using (SqlDataReader reader = SqlHelper.ExecuteReader(sql, System.Data.CommandType.Text))
     {
         if (reader.HasRows)
         {
             while (reader.Read())
             {
                 StudentClass sClass = new StudentClass();
                 sClass.ClassId = reader.GetInt32(0);
                 sClass.ClassName = reader.GetString(1);
                 list.Add(sClass);
             }
         }
     }
     return list;
 }