mysql 索引 null 问题
情况是这样的:
用户表中有这几个字段username
char(16) NOT NULL COMMENT '用户名',password
char(32) NOT NULL COMMENT '密码',email
char(32) NOT NULL COMMENT '用户邮箱',mobile
char(15) NOT NULL COMMENT '用户手机',
username email mobile 是唯一的,所以我想对他们建立唯一索引
但是注册的时候,用户可能只需要手机号码就可以了,不用填邮箱和用户名,此时就有问题了,假如注册只有手机号码,而用户名,邮箱默认空字符串,但是因为有唯一索引,所以插入不了,我想默认设置null ,也就是允许为null 但是又看到这句话:
尽量避免NULL:应该指定列为NOT NULL,除非你想存储NULL。在MySQL中,含有空值的列很难进行查询优化,因为它们使得索引、索引的统计信息以及比较运算更加复杂。你应该用0、一个特殊的值或者一个空串代替空值。
假如我在用户名和邮箱存了null就没有索引了吗,这个字段就不能用索引吗?有性能问题啊?
求大神告诉我这个问题怎么解决
回复内容:
情况是这样的:
用户表中有这几个字段username
char(16) NOT NULL COMMENT '用户名',password
char(32) NOT NULL COMMENT '密码',email
char(32) NOT NULL COMMENT '用户邮箱',mobile
char(15) NOT NULL COMMENT '用户手机',
username email mobile 是唯一的,所以我想对他们建立唯一索引
但是注册的时候,用户可能只需要手机号码就可以了,不用填邮箱和用户名,此时就有问题了,假如注册只有手机号码,而用户名,邮箱默认空字符串,但是因为有唯一索引,所以插入不了,我想默认设置null ,也就是允许为null 但是又看到这句话:
尽量避免NULL:应该指定列为NOT NULL,除非你想存储NULL。在MySQL中,含有空值的列很难进行查询优化,因为它们使得索引、索引的统计信息以及比较运算更加复杂。你应该用0、一个特殊的值或者一个空串代替空值。
假如我在用户名和邮箱存了null就没有索引了吗,这个字段就不能用索引吗?有性能问题啊?
求大神告诉我这个问题怎么解决
在v站上看到的帖子,也许可以帮助你解惑
https://www.v2ex.com/t/60437

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