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)andbit varying(n), wherenis a positive integer.
bittype data must match the lengthnexactly; it is an error to attempt to store shorter or longer bit strings.bit varyingdata is of variable length up to the maximum lengthn; longer strings will be rejected. Writingbitwithout a length is equivalent tobit(1), whilebit varyingwithout a length specification means unlimited length.
Note:If one explicitly casts a bit-string value tobit(n), it will be truncated or zero-padded on the right to be exactlynbits, without raising an error. Similarly, if one explicitly casts a bit-string value tobit varying(n), it will be truncated on the right if it is more thannbits.
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 inSection 8.3for character strings).