NULL) FROM TABLE; -- detect at least one null in rows
</programlisting>

    In some cases, it may be preferable to
    write <replaceable>row</replaceable> <literal>IS DISTINCT FROM NULL</literal>
    or <replaceable>row</replaceable> <literal>IS NOT DISTINCT FROM NULL</literal>,
    which will simply check whether the overall row value is null without any
    additional tests on the row fields.
   </para>

   <para>
    <indexterm>
     <primary>IS TRUE</primary>
    </indexterm>
    <indexterm>
     <primary>IS NOT TRUE</primary>
    </indexterm>
    <indexterm>
     <primary>IS FALSE</primary>
    </indexterm>
    <indexterm>
     <primary>IS NOT FALSE</primary>
    </indexterm>
    <indexterm>
     <primary>IS UNKNOWN</primary>
    </indexterm>
    <indexterm>
     <primary>IS NOT UNKNOWN</primary>
    </indexterm>
    Boolean values can also be tested using the predicates
<synopsis>
<replaceable>boolean_expression</replaceable> IS TRUE
<replaceable>boolean_expression</replaceable> IS NOT TRUE
<replaceable>boolean_expression</replaceable> IS FALSE
<replaceable>boolean_expression</replaceable> IS NOT FALSE
<replaceable>boolean_expression</replaceable> IS UNKNOWN
<replaceable>boolean_expression</replaceable> IS NOT UNKNOWN
</synopsis>
    These will always return true or false, never a null value, even when the
    operand is null.
    A null input is treated as the logical value <quote>unknown</quote>.
    Notice that <literal>IS UNKNOWN</literal> and <literal>IS NOT UNKNOWN</literal> are
    effectively the same as <literal>IS NULL</literal> and
    <literal>IS NOT NULL</literal>, respectively, except that the input
    expression must be of Boolean type.
   </para>

   <para>
    Some comparison-related functions are also available, as shown in <xref
    linkend="functions-comparison-func-table"/>.
   </para>

  <table id="functions-comparison-func-table">
    <title>Comparison Functions</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para>
       <para>
        Example(s)
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>num_nonnulls</primary>
        </indexterm>
        <function>num_nonnulls</function> ( <literal>VARIADIC</literal> <type>"any"</type> )
        <returnvalue>integer</returnvalue>
       </para>
       <para>
        Returns the number of non-null arguments.
       </para>
       <para>
        <literal>num_nonnulls(1, NULL, 2)</literal>
        <returnvalue>2</returnvalue>
       </para></entry>
      </row>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>num_nulls</primary>
        </indexterm>
        <function>num_nulls</function> ( <literal>VARIADIC</literal> <type>"any"</type> )
        <returnvalue>integer</returnvalue>
       </para>
       <para>
        Returns the number of null arguments.
       </para>
       <para>
        <literal>num_nulls(1, NULL, 2)</literal>
        <returnvalue>1</returnvalue>
       </para></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

  </sect1>

  <sect1 id="functions-math">
   <title>Mathematical Functions and Operators</title>

   <para>
    Mathematical operators are provided for many
    <productname>PostgreSQL</productname> types. For types without
    standard mathematical conventions
    (e.g., date/time types) we
    describe the actual behavior in subsequent sections.
   </para>

   <para>
    <xref linkend="functions-math-op-table"/> shows the mathematical
    operators that are available for the standard numeric types.
    Unless otherwise noted, operators shown as
    accepting <replaceable>numeric_type</replaceable> are available for all
    the types <type>smallint</type>, <type>integer</type>,