- 9.1.10.1. The
ucs2Character Set (UCS-2 Unicode Encoding) - 9.1.10.2. The
utf16Character Set (UTF-16 Unicode Encoding) - 9.1.10.3. The
utf32Character Set (UTF-32 Unicode Encoding) - 9.1.10.4. The
utf8Character Set (Three-Byte UTF-8 Unicode Encoding) - 9.1.10.5. The
utf8mb3“Character Set” (Alias forutf8) - 9.1.10.6. The
utf8mb4Character Set (Four-Byte UTF-8 Unicode Encoding)
The initial implementation of Unicode support (in MySQL 4.1) included two character sets for storing Unicode data:
ucs2, the UCS-2 encoding of the Unicode character set using 16 bits per characterutf8, a UTF-8 encoding of the Unicode character set using one to three bytes per character
These two character sets support the characters from the Basic Multilingual Plane (BMP) of Unicode Version 3.0. BMP characters have these characteristics:
Their code values are between 0 and 65535 (or
U+0000..U+FFFF)They can be encoded with a fixed 16-bit word, as in
ucs2They can be encoded with 8, 16, or 24 bits, as in
utf8They are sufficient for almost all characters in major languages
Characters not supported by the aforementioned character sets include supplementary characters that lie outside the BMP. As of MySQL 5.5.3, Unicode support includes supplementary characters, which requires new character sets that have a broader range and therefore take more space. The following table shows a brief feature comparison of previous and current Unicode support.
| Before MySQL 5.5 | MySQL 5.5 and up |
|---|---|
| All Unicode 3.0 characters | All Unicode 5.0 characters |
| No supplementary characters | With supplementary characters |
ucs2 character set, BMP only | No change |
utf8 character set for up to three bytes, BMP only | No change |
New utf8mb4 character set for up to four bytes, BMP
or supplemental | |
New utf16 character set, BMP or supplemental | |
New utf32 character set, BMP or supplemental |
These changes are upward compatible. If you want to use the new
character sets, there are potential incompatibility issues for
your applications; see
Section 9.1.11, “Upgrading from Previous to Current Unicode Support”. That section also
describes how to convert tables from utf8 to
the (four-byte) utf8mb4 character set, and
what constraints may apply in doing so.
MySQL 5.5 supports these Unicode character sets:
ucs2, the UCS-2 encoding of the Unicode character set using 16 bits per characterutf16, the UTF-16 encoding for the Unicode character set; likeucs2but with an extension for supplementary charactersutf32, the UTF-32 encoding for the Unicode character set using 32 bits per characterutf8, a UTF-8 encoding of the Unicode character set using one to three bytes per characterutf8mb4, a UTF-8 encoding of the Unicode character set using one to four bytes per character
ucs2 and utf8 support BMP
characters. utf8mb4,
utf16, and utf32 support
BMP and supplementary characters.
A similar set of collations is available for each Unicode
character set. For example, each has a Danish collation, the
names of which are ucs2_danish_ci,
utf16_danish_ci,
utf32_danish_ci,
utf8_danish_ci, and
utf8mb4_danish_ci. All Unicode collations are
listed at Section 9.1.14.1, “Unicode Character Sets”, which also
describes collation properties for supplementary characters.
Note that 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 need to communicate with the server
using Unicode should set the client character set accordingly;
for example, by issuing a SET NAMES 'utf8'
statement. ucs2, utf16,
and utf32 cannot be used as a client
character set, which means that they do not work for
SET NAMES or SET CHARACTER
SET. (See Section 9.1.4, “Connection Character Sets and Collations”.)
The following sections provide additional detail on the Unicode character sets in MySQL.