gistfile1.php

<?php

$searchFields['Calls']['account_postcode'] = array(
    'query_type' => 'default',
    'operator' => 'subquery',
    'subquery' => 'SELECT id FROM accounts WHERE accounts.deleted=0 AND billing_address_postalcode LIKE',
    'db_field' => array(
        'parent_id',
        ),
    );