- The encoding is the same. That is, the bytes look the same.
- The character set is different. utf8mb4 has more characters.
- The collation (how comparisions are done) is different.
- The perfomance is different, but it rarely matters.
utf8_unicode_ci 意思是,其中仅包括1-、2-和3-byte UTF-8特性。 因此,它排除了大部分Emoji和一些中国特征。
<代码>utf8mb4_unicode_ci系指CHARTER SET utf8mb4为4-byte CHARACTER SET utf8mb4相应。
多年来,统法协会组织一直在发展规格。 这里的地图来自其“转用”至MySQL Collations:
4.0 _unicode_
5.2.0 _unicode_520_ (Unicode 2009; MySQL GA 5.6 2013)
9.0 _0900_
14.0 _uca1400_ai_ci etc. as/ai and cs/ci (MariaDB-10.10, not MySQL)
大部分差异将发生在大多数人从未遇到过的领域。 例如: 在某些时候,一项改变使Emoji得以区别,并以某种方式下达命令。
The suffix (MySQL doc):
_bin -- just compare the bits; don t consider case folding, accents, etc
_ci -- explicitly case insensitive (A=a) and implicitly accent insensitive (a=á)
_ai_ci -- explicitly case insensitive and accent insensitive
_as (etc) -- accent-sensitive (etc)
业绩:
_bin -- simple, fast
_general_ci -- fails to compare multiple letters; eg ss=ß, so somewhat fast
... -- slower
_900_ -- (8.0) much faster because of a rewrite
然而: 核对速度通常是询问中业绩问题最少。 <代码>INDEXes,JOINs, subqueries, table scans, 等对于业绩来说更为关键。
