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sql条件查询+排序

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Jun 07, 2016 pm 04:21 PM

sortconditionInquire

一条sql为: select * from user where gender='1' order by id desc; 加索引方式: 1:为gender添加索引 2:为id添加索引 3:为id和gender添加联合索引事实证明 1是正确的,使用gender索引,这条sql索引级别达到const级别. 如果使用联合索引则达到了index级别实

　　一条sql为:

　　select * from user where gender='1' order by id desc;

　　加索引方式:

　　1:为gender添加索引

　　2:为id添加索引

　　3:为id和gender添加联合索引

　　事实证明

　　1是正确的,使用gender索引,这条sql索引级别达到const级别.

　　如果使用联合索引则达到了index级别

　　实际上运行速度,数据库7w条数据情况下,查询前100条数据

　　1:使用了0.07s

　　2:使用了0.2+s

　　因此,1方式的索引速度更快

，

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