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The PostgreSQL 9.0 Reference Manual - Volume 1A - SQL Language Reference
by The PostgreSQL Global Development Group
Paperback (6"x9"), 454 pages
ISBN 9781906966041
RRP £14.95 ($19.95)

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6.10 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 2.1.2.5 Bit-String Constants for information about the syntax of bit string constants. Bit-logical operators and string manipulation functions are available; see section 7.6 Bit String Functions and Operators.

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 6.3 Character Types for character strings).

ISBN 9781906966041The PostgreSQL 9.0 Reference Manual - Volume 1A - SQL Language ReferenceSee the print edition