PostgreSQL

8.10. Bit String Types
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8.10. Bit String Types

Bit strings are strings of 1’s and 0’s. They can be used to store or visualize bit masks. There are two SQL bit types: bit(`n)` and bit varying(`n), where n` is a positive integer.

bit type data must match the length `n exactly; it is an error to attempt to store shorter or longer bit strings. `bit varying data is of variable length up to the maximum length `n; longer strings will be rejected. Writing `bit without a length is equivalent to bit(1), while bit varying without a length specification means unlimited length.

Note

If one explicitly casts a bit-string value to bit(`n), it will be truncated or zero-padded on the right to be exactly n bits, without raising an error. Similarly, if one explicitly casts a bit-string value to `bit varying(`n), it will be truncated on the right if it is more than n` bits.

Refer to Section 4.1.2.5 for information about the syntax of bit string constants. Bit-logical operators and string manipulation functions are available; see Section 9.6.

Example 8.3. Using the Bit String Types

CREATE TABLE test (a BIT(3), b BIT VARYING(5));
INSERT INTO test VALUES (B'101', B'00');
INSERT INTO test VALUES (B'10', B'101');

ERROR:  bit string length 2 does not match type bit(3)

INSERT INTO test VALUES (B'10'::bit(3), B'101');
SELECT * FROM test;

  a  |  b
-----+-----
 101 | 00
 100 | 101

A bit string value requires 1 byte for each group of 8 bits, plus 5 or 8 bytes overhead depending on the length of the string (but long values may be compressed or moved out-of-line, as explained in Section 8.3 for character strings).

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