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
