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MySQL 9.4 Reference Manual  / ...  / Character Sets, Collations, Unicode  / Unicode Support  /  The utf8mb4 Character Set (4-Byte UTF-8 Unicode Encoding)

12.9.1 The utf8mb4 Character Set (4-Byte UTF-8 Unicode Encoding)

Theutf8mb4 character set has these characteristics:

  • Supports BMP and supplementary characters.

  • Requires a maximum of four bytes per multibyte character.

utf8mb4 contrasts with theutf8mb3 character set, which supports only BMP characters and uses a maximum of three bytes per character:

  • For a BMP character,utf8mb4 andutf8mb3 have identical storage characteristics: same code values, same encoding, same length.

  • For a supplementary character,utf8mb4 requires four bytes to store it, whereasutf8mb3 cannot store the character at all. When convertingutf8mb3 columns toutf8mb4, you need not worry about converting supplementary characters because there are none.

utf8mb4 is a superset ofutf8mb3, so for an operation such as the following concatenation, the result has character setutf8mb4 and the collation ofutf8mb4_col:

SELECT CONCAT(utf8mb3_col, utf8mb4_col);

Similarly, the following comparison in theWHERE clause works according to the collation ofutf8mb4_col:

SELECT * FROM utf8mb3_tbl, utf8mb4_tblWHERE utf8mb3_tbl.utf8mb3_col = utf8mb4_tbl.utf8mb4_col;

For information about data type storage as it relates to multibyte character sets, seeString Type Storage Requirements.