睡月花儿

  • Home
  • About
  • coding
  • Tags86
  • Categories7
  • Posts870
  • Sitemap
  • Commonweal 404
  • Search
  • Table of Contents
  • Overview
戛戛Happy

戛戛Happy

后端, 操作系统, 互联网, 程序开发, Linux, 数据库, MySql, Golang, Ruby
RSS
Creative Commons

select count 使用的索引

Posted on 2015-02-21 In mysql , innodb

在查询select count(*)时,优化器不会使用聚集索引,而是使用辅助索引,因为体积要比聚集索引小,需要的IO操作更少。

  • Post author: 戛戛Happy
  • Post link: https://blog.gagahappy.cn/select-count-second-index/
  • Copyright Notice: All articles in this blog are licensed under BY-NC-SA unless stating additionally.
数据库
慎用With query expansion
Index Condition Pushdown(ICP)优化
京ICP备10044755号
© 2009 – 2024 戛戛Happy
Powered by Hexo & NexT.Gemini