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漫画：什么是Bitmap算法？
source link: https://juejin.im/post/5c4fd2af51882525da267385
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两个月之前——为满足用户标签的统计需求，小灰利用Mysql设计了如下的表结构，每一个维度的标签都对应着Mysql表的一列：要想统计所有90后的程序员该怎么做呢？用一条求交集的SQL语句即可：Select count（distinct Name） as 用户数
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