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9.1.5 Bit-Value Literals

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Bit-value literals are written using b'val' or 0bval notation. val is a binary value written using zeros and ones. Lettercase of any leading b does not matter. A leading 0b is case sensitive and cannot be written as 0B.

Legal bit-value literals:

  1. b'01'
  2. B'01'
  3. 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:

  1. mysql> SELECT b'1000001', CHARSET(b'1000001');
  2. +------------+---------------------+
  3. | b'1000001' | CHARSET(b'1000001') |
  4. +------------+---------------------+
  5. | A          | binary              |
  6. +------------+---------------------+
  7. mysql> SELECT 0b1100001, CHARSET(0b1100001);
  8. +-----------+--------------------+
  9. | 0b1100001 | CHARSET(0b1100001) |
  10. +-----------+--------------------+
  11. | a         | binary             |
  12. +-----------+--------------------+

A 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:

  1. [_charset_name] b'val' [COLLATE collation_name]

Examples:

  1. SELECT _latin1 b'1000001';
  2. SELECT _utf8 0b1000001 COLLATE utf8_danish_ci;

The examples use b'val' notation, but 0bval notation permits introducers as well. For information about introducers, see Section 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 using CAST(... 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:

  1. mysql> SET @v1 = b'1100001';
  2. mysql> SET @v2 = b'1100001'+0;
  3. mysql> SET @v3 = CAST(b'1100001' AS UNSIGNED);
  4. mysql> SELECT @v1, @v2, @v3;
  5. +------+------+------+
  6. | @v1  | @v2  | @v3  |
  7. +------+------+------+
  8. | a    |   97 |   97 |
  9. +------+------+------+

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

  1. mysql> SELECT CHARSET(b''), LENGTH(b'');
  2. +--------------+-------------+
  3. | CHARSET(b'') | LENGTH(b'') |
  4. +--------------+-------------+
  5. | binary       |           0 |
  6. +--------------+-------------+
  7. mysql> SELECT b''+0;
  8. +-------+
  9. | b''+0 |
  10. +-------+
  11. |     0 |
  12. +-------+

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

  1. mysql> CREATE TABLE t (b BIT(8));
  2. mysql> INSERT INTO t SET b = b'11111111';
  3. mysql> INSERT INTO t SET b = b'1010';
  4. 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 as BIN() or HEX(). High-order 0 digits are not displayed in the converted value.

  1. mysql> SELECT b+0, BIN(b), OCT(b), HEX(b) FROM t;
  2. +------+----------+--------+--------+
  3. | b+0  | BIN(b)   | OCT(b) | HEX(b) |
  4. +------+----------+--------+--------+
  5. |  255 | 11111111 | 377    | FF     |
  6. |   10 | 1010     | 12     | A      |
  7. |    5 | 101      | 5      | 5      |
  8. +------+----------+--------+--------+

For bit literals, bit operations are considered numeric context, but bit operations permit numeric or binary string arguments in MySQL 8.0 and higher. To explicitly specify binary string context for bit literals, use a _binary introducer for at least one of the arguments:

  1. mysql> SET @v1 = b'000010101' | b'000101010';
  2. mysql> SET @v2 = _binary b'000010101' | _binary b'000101010';
  3. mysql> SELECT HEX(@v1), HEX(@v2);
  4. +----------+----------+
  5. | HEX(@v1) | HEX(@v2) |
  6. +----------+----------+
  7. | 3F       | 003F     |
  8. +----------+----------+

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.


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Document created the 26/06/2006, last modified the 26/10/2018
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