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MySQL 5.6 Reference Manual  /  ...  /  The utf8mb3 Character Set (3-Byte UTF-8 Unicode Encoding)

10.9.2 The utf8mb3 Character Set (3-Byte UTF-8 Unicode Encoding)

The utfmb3 character set has these characteristics:

  • Supports BMP characters only (no support for supplementary characters)

  • Requires a maximum of three bytes per multibyte character.

Applications that use UTF-8 data but require supplementary character support should use utf8mb4 rather than utf8mb3 (see Section 10.9.1, “The utf8mb4 Character Set (4-Byte UTF-8 Unicode Encoding)”).

Exactly the same set of characters is available in utf8mb3 and ucs2. That is, they have the same repertoire.

utf8 is an alias for utf8mb3; the character limit is implicit, rather than explicit in the name.

utf8mb3 can be used in CHARACTER SET clauses, and utf8mb3_collation_substring in COLLATE clauses, where collation_substring is bin, czech_ci, danish_ci, esperanto_ci, estonian_ci, and so forth. For example:

CREATE TABLE t (s1 CHAR(1) CHARACTER SET utf8mb3;
SELECT * FROM t WHERE s1 COLLATE utf8mb3_general_ci = 'x';
DECLARE x VARCHAR(5) CHARACTER SET utf8mb3 COLLATE utf8mb3_danish_ci;
SELECT CAST('a' AS CHAR CHARACTER SET utf8) COLLATE utf8_czech_ci;

MySQL immediately converts instances of utf8mb3 in statements to utf8, so in statements such as SHOW CREATE TABLE or SELECT CHARACTER_SET_NAME FROM INFORMATION_SCHEMA.COLUMNS or SELECT COLLATION_NAME FROM INFORMATION_SCHEMA.COLUMNS, users will see the name utf8 or utf8_collation_substring.

utf8mb3 is also valid in contexts other than CHARACTER SET clauses. For example:

mysqld --character-set-server=utf8mb3
SET NAMES 'utf8mb3'; /* and other SET statements that have similar effect */
SELECT _utf8mb3 'a';
Tip

To save space with utf8mb3, use VARCHAR instead of CHAR. Otherwise, MySQL must reserve three bytes for each character in a CHAR column that uses utf8mb3 because that is the maximum possible length. For example, MySQL must reserve 30 bytes for a CHAR(10) column that uses utf8mb3.

For additional information about data type storage, see Section 11.7, “Data Type Storage Requirements”. For information about InnoDB physical row storage, including how InnoDB tables that use COMPACT row format handle UTF-8 CHAR(N) columns internally, see Section 14.8.1.2, “The Physical Row Structure of an InnoDB Table”.


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