mysql utf8_general_ci 與 utf8_unicode_ci的區別
For any Unicode character set, operations performed using the xxx_general_cixxx_unicode_ciutf8_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.
譯文
對於任何unicode字元，xxx_general_ci比xxx_unicode_ci速度快。因為xxx_unicode_ci支援類似擴充套件的對映。擴充套件的意思是一個字元等於多個字元的組合。比如在德語中，ß等於ss。xxx_unicode_ci也支援收縮和可忽視字元。xxx_general_ci是傳統的校對規則，它不支援擴充套件、收縮、可忽視字元。它只會一個字元一個字元的比較。
總結
綜上所述，xx_unicode_ci實現了unicode標準，支援擴充套件、可忽視字元等，由於準確性高，所以速度“相對慢”，不過根據現有cpu的效能，已經感覺不出“相對慢”。
xx_general_ci相對古老，是utf8的預設校對規則，由於不是那麼準確，所以速度快。由於是utf8的預設校對規則，所以，我們推薦使用這種校對規則，在開發中，會省去很多麻煩。
參考