integer to a bit string width wider
    than the integer itself will sign-extend on the left.
    Some examples:
<programlisting>
44::bit(10)                    <lineannotation>0000101100</lineannotation>
44::bit(3)                     <lineannotation>100</lineannotation>
cast(-44 as bit(12))           <lineannotation>111111010100</lineannotation>
'1110'::bit(4)::integer        <lineannotation>14</lineannotation>
</programlisting>
    Note that casting to just <quote>bit</quote> means casting to
    <literal>bit(1)</literal>, and so will deliver only the least significant
    bit of the integer.
   </para>
  </sect1>


 <sect1 id="functions-matching">
  <title>Pattern Matching</title>

  <indexterm zone="functions-matching">
   <primary>pattern matching</primary>
  </indexterm>

   <para>
    There are three separate approaches to pattern matching provided
    by <productname>PostgreSQL</productname>: the traditional
    <acronym>SQL</acronym> <function>LIKE</function> operator, the
    more recent <function>SIMILAR TO</function> operator (added in
    SQL:1999), and <acronym>POSIX</acronym>-style regular
    expressions.  Aside from the basic <quote>does this string match
    this pattern?</quote> operators, functions are available to extract
    or replace matching substrings and to split a string at matching
    locations.
   </para>

   <tip>
    <para>
     If you have pattern matching needs that go beyond this,
     consider writing a user-defined function in Perl or Tcl.
    </para>
   </tip>

   <caution>
    <para>
     While most regular-expression searches can be executed very quickly,
     regular expressions can be contrived that take arbitrary amounts of
     time and memory to process.  Be wary of accepting regular-expression
     search patterns from hostile sources.  If you must do so, it is
     advisable to impose a statement timeout.
    </para>

    <para>
     Searches using <function>SIMILAR TO</function> patterns have the same
     security hazards, since <function>SIMILAR TO</function> provides many
     of the same capabilities as <acronym>POSIX</acronym>-style regular
     expressions.
    </para>

    <para>
     <function>LIKE</function> searches, being much simpler than the other
     two options, are safer to use with possibly-hostile pattern sources.
    </para>
   </caution>

   <para>
    <function>SIMILAR TO</function> and <acronym>POSIX</acronym>-style regular
    expressions do not support nondeterministic collations.  If required, use
    <function>LIKE</function> or apply a different collation to the expression
    to work around this limitation.
   </para>

  <sect2 id="functions-like">
   <title><function>LIKE</function></title>

   <indexterm>
    <primary>LIKE</primary>
   </indexterm>

<synopsis>
<replaceable>string</replaceable> LIKE <replaceable>pattern</replaceable> <optional>ESCAPE <replaceable>escape-character</replaceable></optional>
<replaceable>string</replaceable> NOT LIKE <replaceable>pattern</replaceable> <optional>ESCAPE <replaceable>escape-character</replaceable></optional>
</synopsis>

    <para>
     The <function>LIKE</function> expression returns true if the
     <replaceable>string</replaceable> matches the supplied
     <replaceable>pattern</replaceable>.  (As
     expected, the <function>NOT LIKE</function> expression returns
     false if <function>LIKE</function> returns true, and vice versa.
     An equivalent expression is
     <literal>NOT (<replaceable>string</replaceable> LIKE
      <replaceable>pattern</replaceable>)</literal>.)
    </para>

    <para>
     If <replaceable>pattern</replaceable> does not contain percent
     signs or underscores, then the pattern only represents the string
     itself; in that case <function>LIKE</function> acts like the
     equals operator.  An underscore (<literal>_</literal>) in
     <replaceable>pattern</replaceable> stands for (matches) any single
     character; a percent sign (<literal>%</literal>) matches any sequence