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( andn)bit varying(, wheren)n is a positive integer.
bit type data must match the lengthn 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 lengthn; longer strings will be rejected. Writingbit without a length is equivalent tobit(1), whilebit varying without a length specification means unlimited length.
If one explicitly casts a bit-string value tobit(, it will be truncated or zero-padded on the right to be exactlyn)n bits, without raising an error. Similarly, if one explicitly casts a bit-string value tobit varying(, it will be truncated on the right if it is more thann)n bits.
Refer toSection 4.1.2.5 for information about the syntax of bit string constants. Bit-logical operators and string manipulation functions are available; seeSection 9.6.
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 8.3 for character strings).
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