高效分页的SQL技巧(以Oracle为例)-Mysql Tutorial-php.cn

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高效分页的SQL技巧(以Oracle为例)

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Jun 07, 2016 pm 05:41 PM

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一般的分页写法大概就是下面的样子（所谓的三层嵌套写法），SELECT*FROM(SELECTa.*&nbs..

一般的分页写法大概就是下面的样子（所谓的“三层嵌套”写法），

在遇到显示数据表中1百万行以后的记录时，美国服务器，可能会出现性能问题。有人提出的解决方案是利用索引，首先通过扫描索引查出rowid，然后再通过rowid查出所需记录。这样做的问题是如果没有索引怎么办？以Oracle为例，下面是一个更具有一般意义的高效写法：

优化的思想是跳到第1百万位置时只是扫描了rowid，避免了扫描全部字段。当字段个数较多时，速度会有十倍的提升。本例在普通的设备上运行不到1秒就出来结果了。这一方法在千万级或亿级仍然存在问题，其原因在于循环次数并未减少。如果真有rwd这样一个字段，那么通过索引和分区等手段，也能够确保速度。不过，话又说回来，美国空间，分页显示成百上千万条记录这样的事情，虚拟主机，其欲达到的业务目的本身可否有更好的解决之道呢？

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