mysql collation 校对规则 utf8_general_ci 与 utf8_unicode_ci的区别

援引官方文档 Mysql document

For any Unicode character set, operations performed using the xxx_general_ci collation are faster than those for the xxx_unicode_ci collation. For example, comparisons for the utf8_general_ci collation are faster, but slightly less correct, than comparisons for utf8_unicode_ci. The reason for this is that utf8_unicode_ci supports mappings such as expansions; that is, when one character compares as equal to combinations of other characters. For example, in German and some other languages “ß” is equal to “ss”. utf8_unicode_ci also supports contractions and ignorable characters.utf8_general_ci is a legacy collation that does not support expansions, contractions, or ignorable characters. It can make only one-to-one comparisons between characters.

译文

对于任何unicode字符，xxx_general_ci比xxx_unicode_ci速度快。因为xxx_unicode_ci支持类似扩展的映射。扩展的意思是一个字符等于多个字符的组合。比如在德语中，ß等于ss。xxx_unicode_ci也支持收缩和可忽视字符。xxx_general_ci是传统的校对规则，它不支持扩展、收缩、可忽视字符。它只会一个字符一个字符的比较。

总结

综上所述，xx_unicode_ci实现了unicode标准，支持扩展、可忽视字符等，由于准确性高，所以速度“相对慢”，不过根据现有cpu的性能，已经感觉不出“相对慢”。

xx_general_ci相对古老，是utf8的默认校对规则，由于不是那么准确，所以速度快。由于是utf8的默认校对规则，所以，我们推荐使用这种校对规则，在开发中，会省去很多麻烦。

参考

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