- 10.9.1 The utf8mb4 Character Set (4-Byte UTF-8 Unicode Encoding)
- 10.9.2 The utf8mb3 Character Set (3-Byte UTF-8 Unicode Encoding)
- 10.9.3 The utf8 Character Set (Alias for utf8mb3)
- 10.9.4 The ucs2 Character Set (UCS-2 Unicode Encoding)
- 10.9.5 The utf16 Character Set (UTF-16 Unicode Encoding)
- 10.9.6 The utf32 Character Set (UTF-32 Unicode Encoding)
- 10.9.7 Converting Between 3-Byte and 4-Byte Unicode Character Sets
The Unicode Standard includes characters from the Basic Multilingual Plane (BMP) and supplementary characters that lie outside the BMP. This section describes support for Unicode in MySQL. For information about the Unicode Standard itself, visit the Unicode Consortium website.
BMP characters have these characteristics:
Their code point values are between 0 and 65535 (or
They can be encoded in a variable-length encoding using 8, 16, or 24 bits (1 to 3 bytes).
They can be encoded in a fixed-length encoding using 16 bits (2 bytes).
They are sufficient for almost all characters in major languages.
Supplementary characters lie outside the BMP:
Their code point values are between
Unicode support for supplementary characters requires character sets that have a range outside BMP characters and therefore take more space than BMP characters (up to 4 bytes per character).
The UTF-8 (Unicode Transformation Format with 8-bit units) method for encoding Unicode data is implemented according to RFC 3629, which describes encoding sequences that take from one to four bytes. The idea of UTF-8 is that various Unicode characters are encoded using byte sequences of different lengths:
Basic Latin letters, digits, and punctuation signs use one byte.
Most European and Middle East script letters fit into a 2-byte sequence: extended Latin letters (with tilde, macron, acute, grave and other accents), Cyrillic, Greek, Armenian, Hebrew, Arabic, Syriac, and others.
Korean, Chinese, and Japanese ideographs use 3-byte or 4-byte sequences.
MySQL supports these Unicode character sets:
utf8mb4: A UTF-8 encoding of the Unicode character set using one to four bytes per character.
utf8mb3: A UTF-8 encoding of the Unicode character set using one to three bytes per character.
utf8: An alias for
ucs2: The UCS-2 encoding of the Unicode character set using two bytes per character.
utf16: The UTF-16 encoding for the Unicode character set using two or four bytes per character. Like
ucs2but with an extension for supplementary characters.
utf32: The UTF-32 encoding for the Unicode character set using four bytes per character.
Table 10.2, “Unicode Character Set General Characteristics”, summarizes the general characteristics of Unicode character sets supported by MySQL.
Table 10.2 Unicode Character Set General Characteristics
|Character Set||Supported Characters||Required Storage Per Character|
||BMP only||1, 2, or 3 bytes|
||BMP only||2 bytes|
||BMP and supplementary||1, 2, 3, or 4 bytes|
||BMP and supplementary||2 or 4 bytes|
||BMP and supplementary||4 bytes|
Characters outside the BMP compare as REPLACEMENT CHARACTER and
'?' when converted to a Unicode
character set that supports only BMP characters
If you use character sets that support supplementary characters
and thus are “wider” than the BMP-only
sets, there are potential incompatibility issues for your
applications; see Section 10.9.7, “Converting Between 3-Byte and 4-Byte Unicode Character Sets”.
That section also describes how to convert tables from the
utf8mb3 to the (4-byte)
utf8mb4, and what constraints may apply in
A similar set of collations is available for each Unicode
character set. For example, each has a Danish collation, the names
of which are
utf32_danish_ci. For information about Unicode
collations and their differentiating properties, including
collation properties for supplementary characters, see
Section 10.10.1, “Unicode Character Sets”.
Although many of the supplementary characters come from East Asian languages, what MySQL 5.5 adds is support for more Japanese and Chinese characters in Unicode character sets, not support for new Japanese and Chinese character sets.
The MySQL implementation of UCS-2, UTF-16, and UTF-32 stores characters in big-endian byte order and does not use a byte order mark (BOM) at the beginning of values. Other database systems might use little-endian byte order or a BOM. In such cases, conversion of values will need to be performed when transferring data between those systems and MySQL.
MySQL uses no BOM for UTF-8 values.
Client applications that communicate with the server using Unicode
should set the client character set accordingly (for example, by
SET NAMES 'utf8mb4' statement). Some
character sets cannot be used as the client character set.
Attempting to use them with
SET produces an error. See
Impermissible Client Character Sets.
The following sections provide additional detail on the Unicode character sets in MySQL.