CREATE TYPE inventory_item AS (
    name            text,
    supplier_id     integer,
    price           numeric
);

CREATE TABLE on_hand (
    item      inventory_item,
    count     integer
);

INSERT INTO on_hand VALUES (ROW('fuzzy dice',  42 ,  1 . 99 ),  1000 );

CREATE FUNCTION price_extension(inventory_item, integer) RETURNS numeric
AS 'SELECT $1.price * $2' LANGUAGE SQL;

SELECT price_extension(item,  10 ) FROM on_hand;

$dbh->selectall_arrayref(
        'SELECT price_extension( ?, ? ) FROM on_hand',
        undef,
        { 'name' => 'fuzzy dice', 'supplier_id' =>  42 , 'price' =>  1 . 99  },
         10 
);