从服务器上C＃中的SQL数据库中删除旧行

Question

首先，我是SQL的新手，就像今天是全新的。当前，我需要删除早于14天且百分比为0.0的数据行。如果百分比发生变化，我需要保留该行（无论它有多旧），并保持该行的上下。我正在Visual Studio 2013中研究此程序。

如果这是将数据写入服务器的方式：

 public void WriteSystemOnlineHistory()
    {
        //  sql = "create table if not exists SystemOnlineHistory(Online int, Offline int,  Percent Real, dt text)";

        while (true)
        {
            int total  = GetStoreTotals("Total");
            int online = GetStoreTotals("Online");
            int offline = GetStoreTotals("Offline");
            decimal total_dec = (decimal)total ;
            decimal offline_dec = (decimal)offline;
            decimal percent = 100 * (offline_dec / total_dec);
            string dt = this.DateTimeSQLite(DateTime.Now);


            lock (systemUpdateLock)
            {



                string sql = "insert into  SystemOnlineHistory( Online, Offline, Percent,  dt) " +
                                "Values (@Online, @Offline, @Percent, @dt) ";


                using (SQLiteConnection c = new SQLiteConnection(connectionString))
                {

                    SQLiteCommand cmd = c.CreateCommand();
                    cmd.CommandText = sql;


                    cmd.Parameters.AddWithValue("@Online", online);
                    cmd.Parameters.AddWithValue("@Offline", offline);
                    cmd.Parameters.AddWithValue("@Percent", percent);
                    cmd.Parameters.AddWithValue("@dt", dt);


                    c.Open();
                    cmd.ExecuteNonQuery();
                    c.Close();
                }
            }

            Thread.Sleep(new TimeSpan(8, 0, 0));
        }

如何删除旧行？这并不是说我也不能写带有0.0的行，而是只能删除具有14天（或更旧）的0.0的旧行。我希望这是有道理的。我已经对此进行了遗憾的尝试，这里是：

public void RemoveSystemOnlineHistory()
    {
        lock (systemUpdateLock)
        {
            string sql = "delete from SystemOnlineHistory( Online, Offline, Percent, dt) where percent = @percent" + "Values (@Online, @Offline, @Percent, @dt) ";

            using (SQLiteConnection c = new SQLiteConnection(connectionString))
            {
                SQLiteCommand cmd = c.CreateCommand();
                cmd.CommandText = sql;

                cmd.Parameters.AddWithValue("@percent", 0.0);

                c.Open();
                cmd.ExecuteNonQuery();
                c.Close();
            }
        }
    }