MySQL 8.0 Reference Manual Including MySQL NDB Cluster 8.0

10.3.8 Character Set Introducers

A character string literal, hexadecimal literal, or bit-value literal may have an optional character set introducer and COLLATE clause, to designate it as a string that uses a particular character set and collation:

[_charset_name] literal [COLLATE collation_name]

The _charset_name expression is formally called an introducer. It tells the parser, the string that follows uses character set charset_name. An introducer does not change the string to the introducer character set like CONVERT() would do. It does not change the string value, although padding may occur. The introducer is just a signal.

For character string literals, space between the introducer and the string is permitted but optional.

Examples:

SELECT 'abc';
SELECT _latin1'abc';
SELECT _binary'abc';
SELECT _utf8mb4'abc' COLLATE utf8mb4_danish_ci;

SELECT _latin1 X'4D7953514C';
SELECT _utf8mb4 0x4D7953514C COLLATE utf8mb4_danish_ci;

SELECT _latin1 b'1000001';
SELECT _utf8mb4 0b1000001 COLLATE utf8mb4_danish_ci;

Character set introducers and the COLLATE clause are implemented according to standard SQL specifications.

Character string literals can be designated as binary strings by using the _binary introducer. Hexadecimal literals and bit-value literals are binary strings by default, so _binary is permitted, but normally unnecessary. _binary may be useful to preserve a hexadecimal or bit literal as a binary string in contexts for which the literal is otherwise treated as a number. For example, bit operations permit numeric or binary string arguments in MySQL 8.0 and higher, but treat hexadecimal and bit literals as numbers by default. To explicitly specify binary string context for such literals, use a _binary introducer for at least one of the arguments:

mysql> SET @v1 = X'000D' | X'0BC0';
mysql> SET @v2 = _binary X'000D' | X'0BC0';
mysql> SELECT HEX(@v1), HEX(@v2);
+----------+----------+
| HEX(@v1) | HEX(@v2) |
+----------+----------+
| BCD      | 0BCD     |
+----------+----------+

The displayed result appears similar for both bit operations, but the result without _binary is a BIGINT value, whereas the result with _binary is a binary string. Due to the difference in result types, the displayed values differ: High-order 0 digits are not displayed for the numeric result.

MySQL determines the character set and collation of a character string literal, hexadecimal literal, or bit-value literal in the following manner:

Examples:

For character set literals, an introducer indicates the character set for the following string, but does not change how the parser performs escape processing within the string. Escapes are always interpreted by the parser according to the character set given by character_set_connection. For additional discussion and examples, see Section 10.3.6, “Character String Literal Character Set and Collation”.