<literal>atanh(0.5)</literal>
        <returnvalue>0.5493061443340548</returnvalue>
       </para></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

  </sect1>


  <sect1 id="functions-string">
   <title>String Functions and Operators</title>

   <para>
    This section describes functions and operators for examining and
    manipulating string values.  Strings in this context include values
    of the types <type>character</type>, <type>character varying</type>,
    and <type>text</type>.  Except where noted, these functions and operators
    are declared to accept and return type <type>text</type>.  They will
    interchangeably accept <type>character varying</type> arguments.
    Values of type <type>character</type> will be converted
    to <type>text</type> before the function or operator is applied, resulting
    in stripping any trailing spaces in the <type>character</type> value.
   </para>

   <para>
    <acronym>SQL</acronym> defines some string functions that use
    key words, rather than commas, to separate
    arguments.  Details are in
    <xref linkend="functions-string-sql"/>.
    <productname>PostgreSQL</productname> also provides versions of these functions
    that use the regular function invocation syntax
    (see <xref linkend="functions-string-other"/>).
   </para>

   <note>
    <para>
     The string concatenation operator (<literal>||</literal>) will accept
     non-string input, so long as at least one input is of string type, as shown
     in <xref linkend="functions-string-sql"/>.  For other cases, inserting an
     explicit coercion to <type>text</type> can be used to have non-string input
     accepted.
    </para>
   </note>

   <table id="functions-string-sql">
    <title><acronym>SQL</acronym> String Functions and Operators</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function/Operator
       </para>
       <para>
        Description
       </para>
       <para>
        Example(s)
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>character string</primary>
         <secondary>concatenation</secondary>
        </indexterm>
        <type>text</type> <literal>||</literal> <type>text</type>
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Concatenates the two strings.
       </para>
       <para>
        <literal>'Post' || 'greSQL'</literal>
        <returnvalue>PostgreSQL</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <type>text</type> <literal>||</literal> <type>anynonarray</type>
        <returnvalue>text</returnvalue>
       </para>
       <para role="func_signature">
        <type>anynonarray</type> <literal>||</literal> <type>text</type>
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Converts the non-string input to text, then concatenates the two
        strings.  (The non-string input cannot be of an array type, because
        that would create ambiguity with the array <literal>||</literal>
        operators.  If you want to concatenate an array's text equivalent,
        cast it to <type>text</type> explicitly.)
       </para>
       <para>
        <literal>'Value: ' || 42</literal>
        <returnvalue>Value: 42</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>btrim</primary>
        </indexterm>
        <function>btrim</function> ( <parameter>string</parameter> <type>text</type>
        <optional>, <parameter>characters</parameter> <type>text</type> </optional> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Removes the longest string containing only characters