much like a <literal>FOR</literal> loop,
     but instead of iterating through the rows returned by an SQL query,
     it iterates through the elements of an array value.
     (In general, <literal>FOREACH</literal> is meant for looping through
     components of a composite-valued expression; variants for looping
     through composites besides arrays may be added in future.)
     The <literal>FOREACH</literal> statement to loop over an array is:

<synopsis>
<optional> &lt;&lt;<replaceable>label</replaceable>&gt;&gt; </optional>
FOREACH <replaceable>target</replaceable> <optional> SLICE <replaceable>number</replaceable> </optional> IN ARRAY <replaceable>expression</replaceable> LOOP
    <replaceable>statements</replaceable>
END LOOP <optional> <replaceable>label</replaceable> </optional>;
</synopsis>
    </para>

    <para>
     Without <literal>SLICE</literal>, or if <literal>SLICE 0</literal> is specified,
     the loop iterates through individual elements of the array produced
     by evaluating the <replaceable>expression</replaceable>.
     The <replaceable>target</replaceable> variable is assigned each
     element value in sequence, and the loop body is executed for each element.
     Here is an example of looping through the elements of an integer
     array:

<programlisting>
CREATE FUNCTION sum(int[]) RETURNS int8 AS $$
DECLARE
  s int8 := 0;
  x int;
BEGIN
  FOREACH x IN ARRAY $1
  LOOP
    s := s + x;
  END LOOP;
  RETURN s;
END;
$$ LANGUAGE plpgsql;
</programlisting>

     The elements are visited in storage order, regardless of the number of
     array dimensions.  Although the <replaceable>target</replaceable> is
     usually just a single variable, it can be a list of variables when
     looping through an array of composite values (records).  In that case,
     for each array element, the variables are assigned from successive
     columns of the composite value.
    </para>

    <para>
     With a positive <literal>SLICE</literal> value, <literal>FOREACH</literal>
     iterates through slices of the array rather than single elements.
     The <literal>SLICE</literal> value must be an integer constant not larger
     than the number of dimensions of the array.  The
     <replaceable>target</replaceable> variable must be an array,
     and it receives successive slices of the array value, where each slice
     is of the number of dimensions specified by <literal>SLICE</literal>.
     Here is an example of iterating through one-dimensional slices:

<programlisting>
CREATE FUNCTION scan_rows(int[]) RETURNS void AS $$
DECLARE
  x int[];
BEGIN
  FOREACH x SLICE 1 IN ARRAY $1
  LOOP
    RAISE NOTICE 'row = %', x;
  END LOOP;
END;
$$ LANGUAGE plpgsql;

SELECT scan_rows(ARRAY[[1,2,3],[4,5,6],[7,8,9],[10,11,12]]);

NOTICE:  row = {1,2,3}
NOTICE:  row = {4,5,6}
NOTICE:  row = {7,8,9}
NOTICE:  row = {10,11,12}
</programlisting>
    </para>
   </sect2>

   <sect2 id="plpgsql-error-trapping">
    <title>Trapping Errors</title>

    <indexterm>
     <primary>exceptions</primary>
     <secondary>in PL/pgSQL</secondary>
    </indexterm>

    <para>
     By default, any error occurring in a <application>PL/pgSQL</application>
     function aborts execution of the function and the
     surrounding transaction.  You can trap errors and recover
     from them by using a <command>BEGIN</command> block with an
     <literal>EXCEPTION</literal> clause.  The syntax is an extension of the
     normal syntax for a <command>BEGIN</command> block:

<synopsis>
<optional> &lt;&lt;<replaceable>label</replaceable>&gt;&gt; </optional>
<optional> DECLARE
    <replaceable>declarations</replaceable> </optional>
BEGIN
    <replaceable>statements</replaceable>
EXCEPTION
    WHEN <replaceable>condition</replaceable> <optional> OR <replaceable>condition</replaceable> ... </optional> THEN
        <replaceable>handler_statements</replaceable>
    <optional> WHEN <replaceable>condition</replaceable> <optional> OR <replaceable>condition</replaceable> ...