BIT was made with bitfields in mind, not "single" bits. Not that you can not save a single bit, but there is no space saving in this case.
BIT(1) column will occupy one byte per line, as well as a
BIT(8) column. A
BIT(64) column will occupy 8 bytes. A
BIT(59) column will occupy the same 8 bytes, because in any case, would not fit 59 bits in less than 8 bytes.
The manual defines this formula for space estimation: / p>
BIT (M) approximately (M + 7) / 8 bytes
According to documentation , you can have a BIT field with up to 64 bits in length.
As for data entry and return, there is a padding that corresponds to the value defined in the column. If you enter
0b011 in a BIT (6) column, you are actually entering
0b000011 . When reading the data, it will get a value of 6 bits back.
Using a BIT column
To use BIT columns literally, use one of two syntaxes below:
CREATE TABLE t (b BIT(8));
INSERT INTO t SET b = 0b1010;
INSERT INTO t SET b = b'1010';
The returned values are binary strings, if you need them in numerical format, you can force a cast :
mysql> SELECT b+0, BIN(b+0), OCT(b+0), HEX(b+0) FROM t;
| b+0 | BIN(b+0) | OCT(b+0) | HEX(b+0) |
| 255 | 11111111 | 377 | FF |
| 10 | 1010 | 12 | A |
| 5 | 101 | 5 | 5 |
The manual has more details on literals .
There is a article in that mentions many bugs in the BIT type implementation, I do not know how much it is updated.
In addition, there is a discussion in a MySQL bug report that comments that the BIT column is only implemented in MyISAM.
As is an instance of 2005, this may have changed.
Note that the BIT has a relative, which is the SET type, which is saved bit by bit. SET looks like ENUM, but you can save multiple values simultaneously (like tags, for example). SET is for
checkbox as ENUM is for
CREATE TABLE myset (col SET('A', 'B', 'C', 'D'));
INSERT INTO myset (col) VALUES ('A,D')
In this example,
C , and
D occupy one bit each in the database. The% with% of above would be setting 2 of these bits.