MySQL 5.0 supports two character sets for storing Unicode data:
-
ucs2, the UCS-2 Unicode character set. -
utf8, the UTF-8 encoding of the Unicode character set.
In UCS-2 (binary Unicode representation), every character is
represented by a two-byte Unicode code with the most significant
byte first. For example: LATIN CAPITAL LETTER A
has the code 0x0041 and it is stored as a
two-byte sequence: 0x00 0x41. CYRILLIC
SMALL LETTER YERU (Unicode 0x044B) is
stored as a two-byte sequence: 0x04 0x4B. For
Unicode characters and their codes, please refer to the
Unicode Home Page.
Currently, UCS-2 cannot be used as a client character set, which
means that SET NAMES 'ucs2' does not work.
The UTF-8 character set (transform Unicode representation) is an alternative way to store Unicode data. It is implemented according to RFC 3629. The idea of the UTF-8 character set 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 two-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 three-byte sequences.
RFC 3629 describes encoding sequences that take from one to four bytes. Currently, MySQL support for UTF-8 does not include four-byte sequences. (An older standard for UTF-8 encoding is given by RFC 2279, which describes UTF-8 sequences that take from one to six bytes. RFC 3629 renders RFC 2279 obsolete; for this reason, sequences with five and six bytes are no longer used.)
Tip: To save space with UTF-8,
use VARCHAR instead of CHAR.
Otherwise, MySQL must reserve three bytes for each character in a
CHAR CHARACTER SET utf8 column because that is
the maximum possible length. For example, MySQL must reserve 30
bytes for a CHAR(10) CHARACTER SET utf8 column.