刚学完C#，尝试着自己做个QQ。但有两个问题不知道怎么解决。。。

Question

 private void btnAdd_Click(object sender, EventArgs e)
        {
            ///
            ///此处为加载好友信息
            ///
            int friendQQ=0;           //需要用数组
            int friendShipPolicyId=0;
             string sql = string.Format("select * from dbo.Users left outer join dbo.Friends on dbo.Friends.FriendId=dbo.Users.Id where HostId={0}",Convert.ToInt32(UserHelper.Id));
                SqlCommand command = new SqlCommand(sql, DBHelper.connection);
                DBHelper.connection.Open();
               SqlDataReader dataReader = command.ExecuteReader();
                while (dataReader.Read())
                {
                        friendQQ = (int)dataReader["FriendId"];                        ///
                                                                                       ///标记1
                }                                                                      ///
                dataReader.Close();
                DBHelper.connection.Close();//关闭数据库连接
           
            int friendId = 0;//声明变量存储好友QQ号码
            if(tabSearch.SelectedIndex==0)
            {
                if(dgvBasicResult.SelectedRows.Count==0)
                {
                    MessageBox.Show("请选择一个好友！","操作",MessageBoxButtons.OK,MessageBoxIcon.Warning);
                }
                else if(dgvBasicResult.SelectedRows[0].Cells[0]!=null)
                {
                    //获得DataGrideView中的行的第一个单元格的值
                    friendId = int.Parse(dgvBasicResult.SelectedRows[0].Cells[0].Value.ToString());
                    sql = string.Format("select * from dbo.Users where Id={0}",friendId);
                    DBHelper.connection.Open();
                    dataReader = command.ExecuteReader();
                    while (dataReader.Read())                                        ///
                    {                                                                ///标记2
                        friendShipPolicyId = (int)dataReader["FriendshipPolicyId"];  ///
                    }
                    dataReader.Close();//关闭dataReader
                    DBHelper.connection.Close();问题是：
1：在主窗体中加载好友信息时，好友是否重复，重复的就不让显示
2：在获取添加好友的friendShipPolicyId时，没有执行sql语句中搜索的好友的friendShipPolicyId
哪位高手能指点一二？

Answer 1

1.select distinct Users.Id from dbo.Users
 
2.sql = string.Format("select * from dbo.Users where Id={0}",friendId);
  DBHelper.connection.Open();
  command=new SqlCommand(sql, DBHelper.connection);
  dataReader = command.ExecuteReader();

Answer 2

1.select distinct Users.Id from dbo.Users 2.sql = string.Format("select * from dbo.Users where Id={0}",friendId); 
  DBHelper.connection.Open(); 
  command=new SqlCommand(sql, DBHelper.connection); 
  dataReader = command.ExecuteReader();