10.1.10.7 The utf8mb4 Character Set (4-Byte UTF-8 Unicode Encoding)
10.1.10.7 The utf8mb4 Character Set (4-Byte UTF-8 Unicode
Encoding)
The character set named utf8 uses a maximum
of three bytes per character and contains only BMP characters.
The utf8mb4 character set uses a maximum of
four bytes per character supports supplemental characters:
For a BMP character, utf8 and
utf8mb4 have identical storage
characteristics: same code values, same encoding, same
length.
For a supplementary character, utf8
cannot store the character at all, while
utf8mb4 requires four bytes to store
it. Since utf8 cannot store the
character at all, you do not have any supplementary
characters in utf8 columns and you need
not worry about converting characters or losing data when
upgrading utf8 data from older versions
of MySQL.
utf8mb4 is a superset of
utf8, so for an operation such as the
following concatenation, the result has character set
utf8mb4 and the collation of
utf8mb4_col:
SELECT CONCAT(utf8_col, utf8mb4_col);
Similarly, the following comparison in the
WHERE clause works according to the
collation of utf8mb_col:
SELECT * FROM utf8_tbl, utf8mb4_tbl
WHERE utf8_tbl.utf8_col = utf8mb4_tbl.utf8mb4_col;
Tip
To save space with UTF-8, use
VARCHAR instead of
CHAR. Otherwise, MySQL must
reserve three (or four) bytes for each character in a
CHAR CHARACTER SET utf8 (or
utf8mb4) column because that is the
maximum possible length. For example, MySQL must reserve 40
bytes for a CHAR(10) CHARACTER SET
utf8mb4 column.
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