Movatterモバイル変換

Bit-value literals are written usingb'val' or0bval notation.val is a binary value written using zeros and ones. Lettercase of any leadingb does not matter. A leading0b is case-sensitive and cannot be written as0B.

Legal bit-value literals:

b'01'B'01'0b01

Illegal bit-value literals:

b'2'    (2 is not a binary digit)0B01    (0B must be written as 0b)

By default, a bit-value literal is a binary string:

mysql> SELECT b'1000001', CHARSET(b'1000001');+------------+---------------------+| b'1000001' | CHARSET(b'1000001') |+------------+---------------------+| A          | binary              |+------------+---------------------+mysql> SELECT 0b1100001, CHARSET(0b1100001);+-----------+--------------------+| 0b1100001 | CHARSET(0b1100001) |+-----------+--------------------+| a         | binary             |+-----------+--------------------+

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

[_charset_name] b'val' [COLLATEcollation_name]

Examples:

SELECT _latin1 b'1000001';SELECT _utf8 0b1000001 COLLATE utf8_danish_ci;

The examples useb'val' notation, but0bval notation permits introducers as well. For information about introducers, seeSection 10.3.8, “Character Set Introducers”.

In numeric contexts, MySQL treats a bit literal like an integer. To ensure numeric treatment of a bit literal, use it in numeric context. Ways to do this include adding 0 or usingCAST(... AS UNSIGNED). For example, a bit literal assigned to a user-defined variable is a binary string by default. To assign the value as a number, use it in numeric context:

mysql> SET @v1 = b'1100001';mysql> SET @v2 = b'1100001'+0;mysql> SET @v3 = CAST(b'1100001' AS UNSIGNED);mysql> SELECT @v1, @v2, @v3;+------+------+------+| @v1  | @v2  | @v3  |+------+------+------+| a    |   97 |   97 |+------+------+------+

An empty bit value (b'') evaluates to a zero-length binary string. Converted to a number, it produces 0:

mysql> SELECT CHARSET(b''), LENGTH(b'');+--------------+-------------+| CHARSET(b'') | LENGTH(b'') |+--------------+-------------+| binary       |           0 |+--------------+-------------+mysql> SELECT b''+0;+-------+| b''+0 |+-------+|     0 |+-------+

Bit-value notation is convenient for specifying values to be assigned toBIT columns:

mysql> CREATE TABLE t (b BIT(8));mysql> INSERT INTO t SET b = b'11111111';mysql> INSERT INTO t SET b = b'1010';mysql> INSERT INTO t SET b = b'0101';

Bit values in result sets are returned as binary values, which may not display well. To convert a bit value to printable form, use it in numeric context or use a conversion function such asBIN() orHEX(). High-order 0 digits are not displayed in the converted value.

mysql> SELECT b+0, BIN(b), OCT(b), HEX(b) FROM t;+------+----------+--------+--------+| b+0  | BIN(b)   | OCT(b) | HEX(b) |+------+----------+--------+--------+|  255 | 11111111 | 377    | FF     ||   10 | 1010     | 12     | A      ||    5 | 101      | 5      | 5      |+------+----------+--------+--------+