MySQL目录(一)

MySQL索引(一)

数据库开发中索引的使用占了很重要的位置，好的索引会使数据库的读写效率加倍，烂的索引则会拖累整个系统甚至引发灾难。

索引分三类：

index ----普通的索引,数据可以重复

unique ----唯一索引,唯一索引,要求所有记录都唯一

primary key ----主键索引,也就是在唯一索引的基础上相应的列必须为主键

一般的创建索引的语句如下：

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