C＃Mysql查询执行

Question

我想用C＃和mysql执行多个查询，这是我的代码

MySqlConnectionStringBuilder connString = new MySqlConnectionStringBuilder();
            connString.Server = "10.16.106.77";
            connString.Database = "pln";
            connString.UserID = "root";
            connString.Password = "xxxxx";
            connString.IgnorePrepare = false;

            using(MySqlConnection conn = new MySqlConnection(connString.ToString())){
                string cmdText = @"SELECT GROUP_CONCAT(DISTINCT CONCAT('MAX(IF(keterangan = ''',keterangan,''', talenta, NULL)) AS ', QUOTE(keterangan)) ORDER BY keterangan ASC) INTO @sql FROM `data`;
                                    SET @sql = CONCAT('SELECT nip, nama, jabatan,`tanggal jabatan definitif`, unit, jenjang_jabatan, grade_terakhir, tanggal_grade,', @sql, ' FROM data GROUP BY nip');
                                    PREPARE stmt FROM @sql;
                                    EXECUTE stmt";                    

                MySqlCommand cmd = new MySqlCommand(cmdText, conn);
                cmd.Connection.Open();
                using (MySqlDataReader reader = cmd.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        listBox1.Items.Add(reader.GetString("tanggal_grade"));
                    }
                }
            }

它会抛出错误：

@sql必须定义。

请帮忙吗？