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      VB.net 2010 視頻教程 VB.net 2010 視頻教程 VB.net 2010 視頻教程
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      • C#教程之Sql Server 的參數化查詢

      • 2019-04-13 21:26 來源:未知

      為什么要使用參數化查詢呢?參數化查詢寫起來看起來都麻煩,還不如用拼接sql語句來的方便快捷。當然,拼接sql語句執行查詢雖然看起來方便簡潔,其實不然。遠沒有參數化查詢來的安全和快捷。

       

      今天剛好了解了一下關于Sql Server 參數化查詢和拼接sql語句來執行查詢的一點區別。

      參數化查詢與拼接sql語句查詢相比主要有兩點好處:

          1、防止sql注入 

          2、 提高性能(復用查詢計劃)

      首先我們來談下參數化查詢是如何防止sql注入的這個問題吧。

      防注入例子:

        拼接sql語句:

      ("select * from user where name={0}",username)
      
      或者
      
      ("select * from user where name="+username)

      當 name傳進來是一個'aa';Truncate Table user 的時候,這樣會導致直接清除整個表數據

      "select * from user where name='aa';Truncate Table user


        我們使用參數化的時候: 

      ("select * from user where name=@username",new {username=username})


      這時候即使我們傳進來的是'aa';Truncate Table user ,數據庫端也會把這些當做字符串處理,執行的sql語句會變成

      select * from user where name=''aa';Truncate Table user '

      實際上把'aa';Truncate Table user 這個當做了name的值做查詢條件了

      以上就是一個簡單的例子介紹關于參數化查詢如何防止sql注入。

      再看到底是如何提高性能的呢?

      復用查詢計劃:

      select * from AU_User where Id=1
      select * from AU_User where Id=2

      Sql Server在執行一條查詢語句之前都對對它進行“編譯 ”并生成“查詢計劃”,上面兩條查詢語句生成的查詢計劃就是兩條不一樣的查詢計劃,在下面這張圖片當中我們可以去嘗試下執行這兩條sql語句

      ,結果顯而易見會生成兩條查詢計劃,Id后面所接的參數不一致。

       

       

       

       

       

       

       

       

       

       

       

       

       

      然后我們再來看看使用參數化查詢

      select * from AU_User where Id=@Id


      這樣不管你傳的參數是多少,執行編譯生成的查詢計劃都是 select * from AU_User where Id=@Id,這樣可以實現查詢計劃的復用,并不需要同一個查詢去生成多個查詢計劃
      完全可以節省其中生成查詢計劃的時間

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