12.3.1 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_0900_ai_ci and latin1_swedish_ci are collations for the utf8mb4 and latin1 character sets, respectively. The binary character set has a single collation, also named binary, with no suffixes.

• A language-specific collation includes a locale code or language name. For example, utf8mb4_tr_0900_ai_ci and utf8mb4_hu_0900_ai_ci sort characters for the utf8mb4 character set using the rules of Turkish and Hungarian, respectively. utf8mb4_turkish_ci and utf8mb4_hungarian_ci are similar but based on a less recent version of the Unicode Collation Algorithm.

• Collation suffixes indicate whether a collation is case-sensitive, accent-sensitive, or kana-sensitive (or some combination thereof), or binary. The following table shows the suffixes used to indicate these characteristics.

  Table 12.1 Collation Suffix Meanings

  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, and utf8mb4_0900_ai_ci is explicitly case-insensitive 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 the binary 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 information about the differences between the binary collation of the binary character set and the _bin collations of nonbinary character sets, see Section 12.8.5, “The binary Collation Compared to _bin Collations”.

• Collation names for Unicode character sets 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 xxx_general_mysql500_ci collations preserve the pre-5.1.24 ordering of the original xxx_general_ci collations and permit upgrades for tables created before MySQL 5.1.24 (Bug #27877).