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><A
NAME="DATATYPE-BIT"
>8.10. Bit String Types</A
></H1
><P
>    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:
    <TT
CLASS="TYPE"
>bit(<TT
CLASS="REPLACEABLE"
><I
>n</I
></TT
>)</TT
> and <TT
CLASS="TYPE"
>bit
    varying(<TT
CLASS="REPLACEABLE"
><I
>n</I
></TT
>)</TT
>, where
    <TT
CLASS="REPLACEABLE"
><I
>n</I
></TT
> is a positive integer.
   </P
><P
>    <TT
CLASS="TYPE"
>bit</TT
> type data must match the length
    <TT
CLASS="REPLACEABLE"
><I
>n</I
></TT
> exactly; it is an error to attempt to
    store shorter or longer bit strings.  <TT
CLASS="TYPE"
>bit varying</TT
> data is
    of variable length up to the maximum length
    <TT
CLASS="REPLACEABLE"
><I
>n</I
></TT
>; longer strings will be rejected.
    Writing <TT
CLASS="TYPE"
>bit</TT
> without a length is equivalent to
    <TT
CLASS="LITERAL"
>bit(1)</TT
>, while <TT
CLASS="TYPE"
>bit varying</TT
> without a length
    specification means unlimited length.
   </P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>     If one explicitly casts a bit-string value to
     <TT
CLASS="TYPE"
>bit(<TT
CLASS="REPLACEABLE"
><I
>n</I
></TT
>)</TT
>, it will be truncated or
     zero-padded on the right to be exactly <TT
CLASS="REPLACEABLE"
><I
>n</I
></TT
> bits,
     without raising an error.  Similarly,
     if one explicitly casts a bit-string value to
     <TT
CLASS="TYPE"
>bit varying(<TT
CLASS="REPLACEABLE"
><I
>n</I
></TT
>)</TT
>, it will be truncated
     on the right if it is more than <TT
CLASS="REPLACEABLE"
><I
>n</I
></TT
> bits.
    </P
></BLOCKQUOTE
></DIV
><P
>    Refer to <A
HREF="sql-syntax-lexical.html#SQL-SYNTAX-BIT-STRINGS"
>Section 4.1.2.5</A
> for information about the syntax
    of bit string constants.  Bit-logical operators and string
    manipulation functions are available; see <A
HREF="functions-bitstring.html"
>Section 9.6</A
>.
   </P
><DIV
CLASS="EXAMPLE"
><A
NAME="AEN7213"
></A
><P
><B
>Example 8-3. Using the Bit String Types</B
></P
><PRE
CLASS="PROGRAMLISTING"
>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');
<SAMP
CLASS="COMPUTEROUTPUT"
>ERROR:  bit string length 2 does not match type bit(3)</SAMP
>
INSERT INTO test VALUES (B'10'::bit(3), B'101');
SELECT * FROM test;
<SAMP
CLASS="COMPUTEROUTPUT"
>  a  |  b
-----+-----
 101 | 00
 100 | 101</SAMP
></PRE
></DIV
><P
>    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 <A
HREF="datatype-character.html"
>Section 8.3</A
> for character strings).
   </P
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