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10.3.1 Collation Naming Conventions
MySQL collation names follow these conventions:
A collation name starts with the name of the character set with which it is associated, generally followed by one or more suffixes indicating other collation characteristics. For example,
utf8mb4_general_ci
andlatin1_swedish_ci
are collations for theutf8mb4
andlatin1
character sets, respectively. Thebinary
character set has a single collation, also namedbinary
, with no suffixes.A language-specific collation includes a locale code or language name. For example,
utf8mb4_tr_0900_ai_ci
andutf8mb4_hu_0900_ai_ci
sort characters for theutf8mb4
character set using the rules of Turkish and Hungarian, respectively.utf8mb4_turkish_ci
andutf8mb4_hungarian_ci
are similar but based on a less recent version of the Unicode Collation Algorithm.Collation suffixes indicate whether a collation is case and accent sensitive, or binary. The following table shows the suffixes used to indicate these characteristics.
Table 10.1 Collation Case/Accent Sensitivity Suffixes
Suffix Meaning _ai
Accent insensitive _as
Accent sensitive _ci
Case insensitive _cs
Case sensitive _ks
Kana sensitive _bin
Binary For nonbinary collation names that do not specify accent sensitivity, it is determined by case sensitivity. If a collation name does not contain
_ai
or_as
,_ci
in the name implies_ai
and_cs
in the name implies_as
. For example,latin1_general_ci
is explicitly case insensitive and implicitly accent insensitive,latin1_general_cs
is explicitly case sensitive and implicitly accent sensitive, andutf8mb4_0900_ai_ci
is explicitly case and accent insensitive.For Japanese collations, the
_ks
suffix indicates that a collation is kana sensitive; that is, it distinguishes Katakana characters from Hiragana characters. Japanese collations without the_ks
suffix are not kana sensitive and treat Katakana and Hiragana characters equal for sorting.For the
binary
collation of thebinary
character set, comparisons are based on numeric byte values. For the_bin
collation of a nonbinary character set, comparisons are based on numeric character code values, which differ from byte values for multibyte characters. For more information, see Section 10.8.5, “The binary Collation Compared to _bin Collations”.For Unicode character sets, collation names may include a version number to indicate the version of the Unicode Collation Algorithm (UCA) on which the collation is based. UCA-based collations without a version number in the name use the version-4.0.0 UCA weight keys. For example:
utf8mb4_0900_ai_ci
is based on UCA 9.0.0 weight keys (http://www.unicode.org/Public/UCA/9.0.0/allkeys.txt).utf8mb4_unicode_520_ci
is based on UCA 5.2.0 weight keys (http://www.unicode.org/Public/UCA/5.2.0/allkeys.txt).utf8mb4_unicode_ci
(with no version named) is based on UCA 4.0.0 weight keys (http://www.unicode.org/Public/UCA/4.0.0/allkeys-4.0.0.txt).
For Unicode character sets, the
collations preserve the pre-5.1.24 ordering of the originalxxx
_general_mysql500_ci
collations and permit upgrades for tables created before MySQL 5.1.24 (Bug #27877).xxx
_general_ci
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