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MySQL 查询时强制区分大小写

Jun 07, 2016 pm 05:59 PM
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平时很少会考虑数据存储需要明确字符串类型字段的大小写,MySQL默认的查询也不区分大小写。但作为用户信息,一旦用户名重复,又会浪费很多资源。再者,李逵、李鬼的多起来,侦辨起来很困难。要做到这一点,要么在建表时,明确大小写敏感(字段明确大小写敏感

平时很少会考虑数据存储需要明确字符串类型字段的大小写,MySQL默认的查询也不区分大小写。但作为用户信息,一旦用户名重复,又会浪费很多资源。再者,李逵、李鬼的多起来,侦辨起来很困难。要做到这一点,要么在建表时,明确大小写敏感(字段明确大小写敏感)。如果通盘数据库所有字段都需要大小写敏感,不如在字符集设置时做好调整。不过,通常不建议这么做。

如果跟我一样,数据库已经在线上跑了,一个表上百万条数据,做字段类型变更有可能导致数据库宕机。那么好吧,在查询时,多加个单词好了!
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例如,一般查询:

1.SELECT * FROM U WHERE name LIKE 'a%';  
2.SELECT * FROM U WHERE name LIKE 'A%';  其结果是一样的,为了区分'A%'和'a%',可以这么做:

1.SELECT * FROM U WHERE binary name LIKE 'a%';  
2.SELECT * FROM U WHERE binary name LIKE 'A%';  仅仅多了一个binary,就可以得到不同的结果!

当然,如果需要建表时强制区分大小写,可以这么写:

1.create  table  table_name(    
2.     name varchar (20) binary       3.); 
就这么简单!
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