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王雷
lesson plan
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2fdb56fb
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2fdb56fb
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Jan 24, 2019
by
王雷
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Update (SQL)优化分析与方法.md
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(SQL)优化分析与方法.md
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@@ -89,7 +89,7 @@ limit
  
很诧异是不是,和咱们写的 SQL 顺序发生了很大的变化,但却很符合查询的数据处理逻辑,先需要知道在什么地方获取数据,然后根据 on 条件进行数据关联,再通过 where 条件筛选掉不符合条件的数据,接着进行分组、筛选分组结果,然后根据要求在筛选出需要返回的数据项,最后根据取数限定,返回一定量的数据。
  
从 SQL 的执行顺序咱们可以看出,这就是
要给
在逐渐筛选数据的过程,一步一步的减少最终返回的数据量,而这也正是我们优化 SQL 的目标,让能大量减少数据量的筛选条件先执行,然后逐步细化调整;
  
从 SQL 的执行顺序咱们可以看出,这就是
一个
在逐渐筛选数据的过程,一步一步的减少最终返回的数据量,而这也正是我们优化 SQL 的目标,让能大量减少数据量的筛选条件先执行,然后逐步细化调整;
  
常用的 SQL 优化方法如下:
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