<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> <optional> CONSTANT </optional> <replaceable>type</replaceable> <optional> COLLATE <replaceable>collation_name</replaceable> </optional> <optional> NOT NULL </optional> <optional> { DEFAULT | := | = } <replaceable>expression</replaceable> </optional>;
</synopsis>
      The <literal>DEFAULT</literal> clause, if given, specifies the initial value assigned
      to the variable when the block is entered.  If the <literal>DEFAULT</literal> clause
      is not given then the variable is initialized to the
      <acronym>SQL</acronym> null value.
      The <literal>CONSTANT</literal> option prevents the variable from being
      assigned to after initialization, so that its value will remain constant
      for the duration of the block.
      The <literal>COLLATE</literal> option specifies a collation to use for the
      variable (see <xref linkend="plpgsql-declaration-collation"/>).
      If <literal>NOT NULL</literal>
      is specified, an assignment of a null value results in a run-time
      error. All variables declared as <literal>NOT NULL</literal>
      must have a nonnull default value specified.
      Equal (<literal>=</literal>) can be used instead of PL/SQL-compliant
      <literal>:=</literal>.
     </para>

     <para>
      A variable's default value is evaluated and assigned to the variable
      each time the block is entered (not just once per function call).
      So, for example, assigning <literal>now()</literal> to a variable of type
      <type>timestamp</type> causes the variable to have the
      time of the current function call, not the time when the function was
      precompiled.
     </para>

     <para>
      Examples:
<programlisting>
quantity integer DEFAULT 32;
url varchar := 'http://mysite.com';
transaction_time CONSTANT timestamp with time zone := now();
</programlisting>
     </para>

     <para>
      Once declared, a variable's value can be used in later initialization
      expressions in the same block, for example:
<programlisting>
DECLARE
  x integer := 1;
  y integer := x + 1;
</programlisting>
     </para>

    <sect2 id="plpgsql-declaration-parameters">
     <title>Declaring Function Parameters</title>

     <para>
      Parameters passed to functions are named with the identifiers
      <literal>$1</literal>, <literal>$2</literal>,
      etc.  Optionally, aliases can be declared for
      <literal>$<replaceable>n</replaceable></literal>
      parameter names for increased readability.  Either the alias or the
      numeric identifier can then be used to refer to the parameter value.
     </para>

     <para>
      There are two ways to create an alias.  The preferred way is to give a
      name to the parameter in the <command>CREATE FUNCTION</command> command,
      for example:
<programlisting>
CREATE FUNCTION sales_tax(subtotal real) RETURNS real AS $$
BEGIN
    RETURN subtotal * 0.06;
END;
$$ LANGUAGE plpgsql;
</programlisting>
      The other way is to explicitly declare an alias, using the
      declaration