高手给个好用的web service代码吧

Question

[WebMethod(Description = "内容信息")]
        public string ContentInfo(string param)
        {
            string total = "";
            string result_head = "<contents>";
            string result_foot = "</contents>";
            string result = "";
            string query = "select * from talk left join reply on talk.id='"+param+"' and reply.rid='"+param+"' where reply.rid is not null";
            MySqlConnection myConnection = new MySqlConnection("server=localhost;user=xxxx;password=xxx;database=xxx;charset=utf8");
            DataSet ds = new DataSet();
            DataTable dtable;
            DataRowCollection dc;
            DataRow drow;
            myConnection.Open();
            MySqlDataAdapter sqld = new MySqlDataAdapter(query, myConnection);
            sqld.Fill(ds, "con");
            dtable = ds.Tables["con"];
            dc = dtable.Rows;
            if (dc.Count == 0)
            {
//运行这里的查询出错
                ds.Clear();
                MySqlDataAdapter sqld2 = new MySqlDataAdapter("select *  from talk,reply  where talk.id='" + param + "' and reply.fuzhuid=1", myConnection);
                sqld2.Fill(ds, "con2");
                DataTable dtable2 = ds.Tables["con2"];
                DataRowCollection dc2 = dtable2.Rows;
                dc2 = dtable2.Rows;
                for (int i = 0; i < dc2.Count; i++)
                {
                    DataRow drow2 = dc2[i];
                    //此处省略
                }
                total = result_head + result + result_foot;            
            }
            else
            {
//运行这里的查询没问题，正常显示数据
                for (int i = 0; i < dc.Count; i++)
                {
                    drow = dc[i];
                   //此处省略
                }
                total = result_head + result + result_foot;
                myConnection.Close();
            }
            return total;
        }为什么会错啊有什么好的代码替换替换