type</secondary>
   </indexterm>

   <para>
    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:
    <type>bit(<replaceable>n</replaceable>)</type> and <type>bit
    varying(<replaceable>n</replaceable>)</type>, where
    <replaceable>n</replaceable> is a positive integer.
   </para>

   <para>
    <type>bit</type> type data must match the length
    <replaceable>n</replaceable> exactly; it is an error to attempt to
    store shorter or longer bit strings.  <type>bit varying</type> data is
    of variable length up to the maximum length
    <replaceable>n</replaceable>; longer strings will be rejected.
    Writing <type>bit</type> without a length is equivalent to
    <literal>bit(1)</literal>, while <type>bit varying</type> without a length
    specification means unlimited length.
   </para>

   <note>
    <para>
     If one explicitly casts a bit-string value to
     <type>bit(<replaceable>n</replaceable>)</type>, it will be truncated or
     zero-padded on the right to be exactly <replaceable>n</replaceable> bits,
     without raising an error.  Similarly,
     if one explicitly casts a bit-string value to
     <type>bit varying(<replaceable>n</replaceable>)</type>, it will be truncated
     on the right if it is more than <replaceable>n</replaceable> bits.
    </para>
   </note>

   <para>
    Refer to <xref
    linkend="sql-syntax-bit-strings"/> for information about the syntax
    of bit string constants.  Bit-logical operators and string
    manipulation functions are available; see <xref
    linkend="functions-bitstring"/>.
   </para>

   <example>
    <title>Using the Bit String Types</title>

<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');
<computeroutput>
ERROR:  bit string length 2 does not match type bit(3)
</computeroutput>
INSERT INTO test VALUES (B'10'::bit(3), B'101');
SELECT * FROM test;
<computeroutput>
  a  |  b
-----+-----
 101 | 00
 100 | 101
</computeroutput>
</programlisting>
   </example>

   <para>
    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 <xref linkend="datatype-character"/> for character strings).
   </para>
  </sect1>

  <sect1 id="datatype-textsearch">
   <title>Text Search Types</title>

   <indexterm zone="datatype-textsearch">
    <primary>full text search</primary>
    <secondary>data types</secondary>
   </indexterm>

   <indexterm zone="datatype-textsearch">
    <primary>text search</primary>
    <secondary>data types</secondary>
   </indexterm>

   <para>
    <productname>PostgreSQL</productname> provides two data types that
    are designed to support full text search, which is the activity of
    searching through a collection of natural-language <firstterm>documents</firstterm>
    to locate those that best match a <firstterm>query</firstterm>.
    The <type>tsvector</type> type represents a document in a form optimized
    for text search; the <type>tsquery</type> type similarly represents
    a text query.
    <xref linkend="textsearch"/> provides a detailed explanation of this
    facility, and <xref linkend="functions-textsearch"/> summarizes the
    related functions and operators.
   </para>

   <sect2 id="datatype-tsvector">
    <title><type>tsvector</type></title>

    <indexterm>
     <primary>tsvector (data type)</primary>
    </indexterm>

    <para>
     A <type>tsvector</type> value is a sorted list of distinct
     <firstterm>lexemes</firstterm>, which are words that have been
     <firstterm>normalized</firstterm> to merge different variants of the same word
     (see <xref linkend="textsearch"/> for details).  Sorting and
     duplicate-elimination are done automatically during input, as shown in
     this example:

<programlisting>