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 varying(, 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 varying without a length specification means unlimited length.
If one explicitly casts a bit-string value to
bit(, 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(, it will be truncated on the right if it is more than
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).