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.
Note: Prior to PostgreSQL 7.2, BIT data
was always silently truncated or zero-padded on the right, with
or without an explicit cast. This was changed to comply with the
SQL standard.
Refer to Section 1.1.2.2 for information about the syntax
of bit string constants. Bit-logical operators and string
manipulation functions are available; see Chapter 6.
Example 5-3. 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
