ASP.NET-C#與MySQL連接遇到問題Fatal error encountered during command execution

最近架了個MySQL Server，用mysql workbench都連得到，但用C#程式要連時，跳出以下錯誤
Fatal error encountered during command execution

後來查了一下，在connectstring中加了"Allow User Variables=True;"就解決了
連線字串可參考(config)
<add key="ConnString" value="SERVER = xxx.xx.xxx.xx; DATABASE = xxx; User ID = xxx; PASSWORD = xxxxxxxx; SslMode=none; Connect Timeout=3600;Allow User Variables=True;" />

程式後端可這樣讀string，並抓資料

        public static DataTable GetData(string sql)
        {
            //連接字串
            String conString = System.Configuration.ConfigurationManager.AppSettings["ConnString"];
            //取得MySQLConnection
            MySqlConnection conn = new MySqlConnection();

            conn.ConnectionString = conString;

            DataTable dt = new DataTable();
            MySqlDataAdapter adapter = new MySqlDataAdapter(sql, conn);
            adapter.Fill(dt);
            return dt;
        }