C# mysql 带参数语句

CREATE TABLE `数据` (
  `createtime` datetime NOT NULL,
  `dt` datetime NOT NULL,
  `val` float(7,2) DEFAULT NULL,
  PRIMARY KEY (`createtime`,`dt`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

public static void Save(DateTime createtime, List<DtVal> dvs)
{
    string sql = "INSERT INTO 数据 (createtime, dt, val) VALUES(‘" + createtime.ToString("yyyy-MM-dd HH:mm:ss") + "‘, @p1,@p2);";
    using (MySqlConnection conn = new MySqlConnection(connStr))
    {
        conn.Open();
        using (MySqlCommand cmd = conn.CreateCommand())
        {
            cmd.CommandText = sql;
            cmd.Prepare();
　　　　　　　for (int i = 0; i < dvs.Count; i++)
            {
                cmd.Parameters.Clear();
                MySql.Data.Types.MySqlDateTime time = new MySql.Data.Types.MySqlDateTime(dvs[i].time);//注意：日期特殊处理
                cmd.Parameters.AddWithValue("p1", time);
                cmd.Parameters.AddWithValue("p2", dvs[i].val);
                cmd.ExecuteNonQuery();
            }
        }
    }
}