有没有一种简单的查找数据唯一性的解决方案？
比如注册网站显示“该用户名已被使用”，“该邮箱已被使用”，都是通过Ajax在后台去查找该用户名或邮箱在mysql中是否存在，有没有一种简单的方法，不用mysql，能够迅速在大数据中查找一个数据如用户名或邮箱是否已经存在了？
回复内容：
比如注册网站显示“该用户名已被使用”，“该邮箱已被使用”，都是通过Ajax在后台去查找该用户名或邮箱在mysql中是否存在，有没有一种简单的方法，不用mysql，能够迅速在大数据中查找一个数据如用户名或邮箱是否已经存在了？
好久不见。不和后台通讯当然是不行的，查询结果又不可能凭空产生出来。不过这个需求确实未必需要全功能的sql数据库。
你可以在系统本身采用mysql不变的情况下，再加一套redis缓存系统内所有的用户名（或其他需要唯一的条目）以备快速查询。
redis的底层是哈希表，哈希表的效率可以说是不能超越的。而数据量巨大时，redis更可以直接支持分布式部署，分库和平摊完全无需用户编程，非常便利。
当然具体方案全看你的应用实例而定。不过除了“数据太少无需缓存”和“数据够多直接上redis”之外，我很难想到其他更优的方案。
如果沒索引, 最坏情况是O(n)過一遍, 這在生產環境是不能接受的
所以總歸要有索引, 這個索引是用關係數據庫還是另外的東西可以商量
如果只是要快速判断用户名是否存在，用redis是最简单的方法
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