SQL Server 性能优化之T-SQL NOT IN 和 NOT Exists-Mysql Tutorial-php.cn

SQL Server 性能优化之T-SQL NOT IN 和 NOT Exists

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Release： 2016-06-07 15:12:50

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这次介绍一下T-SQL中Not IN 和Not Exists的优化。 Not IN 和 Not Exists 命令 : 有些情况下，需要select/update/delete 操作孤立数据。孤立数据：不存在主表中而存在其关联表中。操作这样的数据，一般第一反应是利用Not in 或 Not Exists命令。使用Not IN

这次介绍一下T-SQL中“Not IN” 和“Not Exists”的优化。

Not IN 和 Not Exists 命令 :

有些情况下，需要select/update/delete 操作孤立数据。孤立数据：不存在主表中而存在其关联表中。

操作这样的数据，一般第一反应是利用“Not in” 或 “Not Exists”命令。使用Not IN会严重影响性能，因为这个命令会逐一检查每个记录，就会造成资源紧张，尤其是当对大数据进行更新和删除操作时，可能导致资源被这些操作锁住。

选择NOT IN 还是 NOT Exists

现在SQL Server 中有两个命令可以使用大数据的插入、更新、删除操作，不仅性能方面比NOT IN 和 NOT Exists有很大的提高，而且语法简单，写出来的语句看上去也很清爽。现在就请它们闪亮登场，Merge 和 Except。

例子:

首先创建两个表

<span class="lnum">   1:  </span><span class="kwrd">use</span> [MyTest]

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<span class="lnum">   2:  </span><span class="kwrd">Create</span> <span class="kwrd">table</span> Test1 (name <span class="kwrd">varchar</span> (100) )

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<span class="lnum">   3:  </span><span class="kwrd">Create</span> <span class="kwrd">table</span> Test2 (name <span class="kwrd">varchar</span> (100) )

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使用Not IN命令Select/update/delete操作：

<span class="lnum">   1:  </span><span class="kwrd">SELECT</span> name <span class="kwrd">FROM</span> Test1 <span class="kwrd">where</span> name <span class="kwrd">not</span> <span class="kwrd">in</span> (<span class="kwrd">select</span> name <span class="kwrd">from</span> Test2)

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<span class="lnum">   2:  </span><span class="kwrd">UPDATE</span> Test1 <span class="kwrd">SET</span> name =N<span class="str">'Company_Name'</span> <span class="kwrd">where</span> name <span class="kwrd">not</span> <span class="kwrd">in</span> (<span class="kwrd">select</span> name <span class="kwrd">from</span> Test2)

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<span class="lnum">   3:  </span><span class="kwrd">DELETE</span> Test1 <span class="kwrd">FROM</span> Test1 <span class="kwrd">where</span> name <span class="kwrd">not</span> <span class="kwrd">in</span> (<span class="kwrd">select</span> name <span class="kwrd">from</span> Test2)

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使用性能更好的Merge and Except：

<span class="lnum">   1:  </span>merge Test1 T <span class="kwrd">using</span> (<span class="kwrd">select</span> name <span class="kwrd">from</span> Test1 <span class="kwrd">except</span> <span class="kwrd">select</span> name <span class="kwrd">from</span> Test2 )S <span class="kwrd">on</span> t.name=s.name

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<span class="lnum">   2:  </span><span class="kwrd">when</span> matched <span class="kwrd">then</span> <span class="kwrd">update</span> <span class="kwrd">SET</span> name=N<span class="str">'New_Name'</span> ;

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<span class="lnum">   3:  </span>merge Test1 T <span class="kwrd">using</span> (<span class="kwrd">select</span> name <span class="kwrd">from</span> Test1 <span class="kwrd">except</span> <span class="kwrd">select</span> name <span class="kwrd">from</span> Test2 )S <span class="kwrd">on</span> t.name=s.name

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<span class="lnum">   4:  </span><span class="kwrd">when</span> matched <span class="kwrd">then</span> <span class="kwrd">delete</span> ;

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<span class="lnum">   5:  </span><span class="kwrd">SELECT</span> * <span class="kwrd">FROM</span> Test1 S <span class="kwrd">where</span> <span class="kwrd">not</span> <span class="kwrd">exists</span> (<span class="kwrd">select</span> 1 <span class="kwrd">from</span> Test1 <span class="kwrd">inner</span> <span class="kwrd">join</span> Test2 <span class="kwrd">on</span> Test1.name=Test2.name <span class="kwrd">and</span> Test1.name=s.name)

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注意，上面还是有一部分使用了Not Exists：

<span class="lnum">   1:  </span><span class="kwrd">SELECT</span> * <span class="kwrd">FROM</span> Test1 S <span class="kwrd">where</span> <span class="kwrd">not</span> <span class="kwrd">exists</span> (<span class="kwrd">select</span> 1 <span class="kwrd">from</span> Test1 <span class="kwrd">inner</span> <span class="kwrd">join</span> Test2 <span class="kwrd">on</span> Test1.name=Test2.name <span class="kwrd">and</span> Test1.name=s.name)

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现在需要使用高效的Except：

<span class="lnum">   1:  </span><span class="kwrd">select</span> name <span class="kwrd">from</span> Test1 <span class="kwrd">except</span> <span class="kwrd">select</span> name <span class="kwrd">from</span> Test2

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在这里只是给出了例子，没有拿出实际的对比数据。但是Merge 和Except 两个命令在大数据的处理方面的性能，要比

Not IN 和Not EXISTS 好很多。不管你信不信，反正我信了！！！

在此谢谢读完这篇博客，有什么写的不对的地方请指正

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