converted to lower case
     unless double-quoted, just as they are in ordinary SQL commands.
    </para>

    <para>
     Comments work the same way in <application>PL/pgSQL</application> code as in
     ordinary SQL.  A double dash (<literal>--</literal>) starts a comment
     that extends to the end of the line. A <literal>/*</literal> starts a
     block comment that extends to the matching occurrence of
     <literal>*/</literal>.  Block comments nest.
    </para>

    <para>
     Any statement in the statement section of a block
     can be a <firstterm>subblock</firstterm>.  Subblocks can be used for
     logical grouping or to localize variables to a small group
     of statements.  Variables declared in a subblock mask any
     similarly-named variables of outer blocks for the duration
     of the subblock; but you can access the outer variables anyway
     if you qualify their names with their block's label. For example:
<programlisting>
CREATE FUNCTION somefunc() RETURNS integer AS $$
&lt;&lt; outerblock &gt;&gt;
DECLARE
    quantity integer := 30;
BEGIN
    RAISE NOTICE 'Quantity here is %', quantity;  -- Prints 30
    quantity := 50;
    --
    -- Create a subblock
    --
    DECLARE
        quantity integer := 80;
    BEGIN
        RAISE NOTICE 'Quantity here is %', quantity;  -- Prints 80
        RAISE NOTICE 'Outer quantity here is %', outerblock.quantity;  -- Prints 50
    END;

    RAISE NOTICE 'Quantity here is %', quantity;  -- Prints 50

    RETURN quantity;
END;
$$ LANGUAGE plpgsql;
</programlisting>
    </para>

    <note>
     <para>
      There is actually a hidden <quote>outer block</quote> surrounding the body
      of any <application>PL/pgSQL</application> function.  This block provides the
      declarations of the function's parameters (if any), as well as some
      special variables such as <literal>FOUND</literal> (see
      <xref linkend="plpgsql-statements-diagnostics"/>).  The outer block is
      labeled with the function's name, meaning that parameters and special
      variables can be qualified with the function's name.
     </para>
    </note>

    <para>
     It is important not to confuse the use of
     <command>BEGIN</command>/<command>END</command> for grouping statements in
     <application>PL/pgSQL</application> with the similarly-named SQL commands
     for transaction
     control.  <application>PL/pgSQL</application>'s <command>BEGIN</command>/<command>END</command>
     are only for grouping; they do not start or end a transaction.
     See <xref linkend="plpgsql-transactions"/> for information on managing
     transactions in <application>PL/pgSQL</application>.
     Also, a block containing an <literal>EXCEPTION</literal> clause effectively
     forms a subtransaction that can be rolled back without affecting the
     outer transaction.  For more about that see <xref
     linkend="plpgsql-error-trapping"/>.
    </para>
  </sect1>

  <sect1 id="plpgsql-declarations">
    <title>Declarations</title>

    <para>
     All variables used in a block must be declared in the
     declarations section of the block.
     (The only exceptions are that the loop variable of a <literal>FOR</literal> loop
     iterating over a range of integer values is automatically declared as an
     integer variable, and likewise the loop variable of a <literal>FOR</literal> loop
     iterating over a cursor's result is automatically declared as a
     record variable.)
    </para>

    <para>
     <application>PL/pgSQL</application> variables can have any SQL data type, such as
     <type>integer</type>, <type>varchar</type>, and
     <type>char</type>.
    </para>

    <para>
     Here are some examples of variable declarations:
<programlisting>
user_id integer;
quantity numeric(5);
url varchar;
myrow tablename%ROWTYPE;
myfield tablename.columnname%TYPE;
arow RECORD;
</programlisting>
    </para>

    <para>
     The general syntax of a variable declaration is:
<synopsis>
<replaceable>name</replaceable>