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, utf8_general_ci and latin1_swedish_ci are collations for the utf8 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 language name. For example, utf8_turkish_ci and utf8_hungarian_ci sort characters for the utf8 character set using the rules of Turkish and Hungarian, respectively.

• 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 10.1 Collation Suffix Meanings

  Suffix	Meaning
  _ai	Accent-insensitive
  _as	Accent-sensitive
  _ci	Case-insensitive
  _cs	Case-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, and latin1_general_cs is explicitly case-sensitive and implicitly accent-sensitive.

  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 10.8.5, “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:

  • utf8_unicode_520_ci is based on UCA 5.2.0 weight keys (http://www.unicode.org/Public/UCA/5.2.0/allkeys.txt).

  • utf8_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).