PostgreSQL 7.2.1 Documentation
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3.9. Bit String Types

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(x) and BIT VARYING(x); where x is a positive integer.

BIT type data must match the length x exactly; it is an error to attempt to store shorter or longer bit strings. BIT VARYING is of variable length up to the maximum length x; longer strings will be rejected. BIT without length is equivalent to BIT(1), BIT VARYING without length specification means unlimited length.

Note: Prior to PostgreSQL 7.2, BIT type data was zero-padded on the right. This was changed to comply with the SQL standard. To implement zero-padded bit strings, a combination of the concatenation operator and the substring function can be used.

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 4.

Example 3-3. 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 does not match type bit(3)
SELECT SUBSTRING(b FROM 1 FOR 2) FROM test;
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