PostgreSQL 7.1.3 Documentation
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# 3.8. 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`)`; the `x` specifies the maximum length. `BIT` type data is automatically padded with 0's on the right to the maximum length, `BIT VARYING` is of variable length. `BIT` without length is equivalent to `BIT(1)`, `BIT VARYING` means unlimited length. Input data that is longer than the allowed length will be truncated. 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.

Some examples:

    CREATE TABLE test (a BIT(3), b BIT VARYING(5));
    INSERT INTO test VALUES (B'101', B'00');
    SELECT SUBSTRING(b FROM 1 FOR 2) FROM test;

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