-- 假設 OrderDetailId 是 varchar(20)

-- OrderDetail 有千萬筆資料



Select * from OrderDetail where OrderDetailId= N'20220923084533'

-- 結果跑超級久 (未使用 PK 找，掃整個 table)

Select * from OrderDetail where OrderDetailId= '20220923084533'

-- 結果一下就出來 (使用 PK 找)

-- **資料庫設計最好以數值來當 key 比較好

var newFilename = filename.Replace("..", "").ValidFilenameCharacters();

        static System.Security.Cryptography.RandomNumberGenerator RandomNumberGenerator = null;



        /// <summary>

        /// 回傳大於等於 0 小於 1

        /// </summary>

        /// <returns></returns>

        public static double NextDouble()

        {

            if (RandomNumberGenerator == null || LastRandomGenerateTime < DateTime.Now.AddMinutes(-1))

            {

                RandomNumberGenerator = System.Security.Cryptography.RandomNumberGenerator.Create();

            }



            // Generate four random bytes

            byte[] four_bytes = new byte[4];

            RandomNumberGenerator.GetBytes(four_bytes);



            // Convert the bytes to a UInt32

            uint scale = BitConverter.ToUInt32(four_bytes, 0);



            // And use that to pick a random number >= min and < max

            // 0 <= (scale / (uint.MaxValue + 1.0)) < 1

            return scale / (uint.MaxValue + 1.0);

        }



        /// <summary>

        /// 回傳值介於 min ~ (max - 1)

        /// </summary>

        /// <param name="min"></param>

        /// <param name="max"></param>

        /// <returns></returns>

        public static int GetRandomInt(int min, int max)

        {

            if(max < min)

            {

                throw new Exception("最大值不可小於最小值");

            }



            // Generate four random bytes

            byte[] four_bytes = new byte[4];

            RandomNumberGenerator.GetBytes(four_bytes);



            // And use that to pick a random number >= min and < max

            return (int)(min + (max - min) * NextDouble()); //因為 NextDouble 會小於 1，所以用無條件捨去.

        }



        /// <summary>

        /// 產生 0 ~ (max - 1) 的亂數

        /// </summary>

        /// <param name="max"></param>

        /// <returns></returns>

        public static int GetRandomInt(int max)

        {

            return GetRandomInt(0, max);

        }



        /// <summary>

        /// 產生 0 ~ (int.MaxValue - 1) 的亂數

        /// </summary>

        /// <returns></returns>

        public static int GetRandomInt()

        {

            return GetRandomInt(int.MaxValue);

        }

public static void UpdateTableCache()

{

    //標記自已是正在執行的 Thread. 讓舊的 Thread 在執行完畢之後, 應該會自動結束. 以防舊的 Thread 執行超過 10 秒.

    CurrentThreadId = System.Threading.Thread.CurrentThread.ManagedThreadId;



    try

    {

        //確認自已是正在執行的 Thread, 重覆執行. (另一個 Thread 插入執行)

        while (CurrentThreadId == System.Threading.Thread.CurrentThread.ManagedThreadId)

        {

            LastUpdateDate = DateTime.Now;



            foreach (var dbId in CachedDbs)

            {

                var sql = @"select * from table_monitor";



                var dt = Su.PgSql.DtFromSql(sql, dbId);



                foreach (DataRow row in dt.Rows)

                {

                    string changeId = row["update_count"].DBNullToDefault();

                    string CacheKey = TableCacheKey(dbId, row["table_name"].DBNullToDefault());

                    ObjectCache cache = MemoryCache.Default;



                    string OldValue = (string)cache[CacheKey];



                    if (OldValue == null)

                    {

                        cache.Set(CacheKey, changeId, DateTime.MaxValue);

                    }

                    else

                    {

                        if (changeId != OldValue)

                        {

                            cache.Remove(CacheKey);

                            cache.Set(CacheKey, changeId, DateTime.MaxValue);

                        }

                    }

                }

            }



            //每兩秒檢查一次

            System.Threading.Thread.Sleep(2000);

        }

    }

    catch (Exception)

    {

        //依經驗, 只要 DB 能通, 這裡幾乎不會有問題, 所以這裡暫時不處理, 未來有問題時可以考慮寫入文字檔比較好.

    }

}