* @param string $baseKey Field name to match the base-level keys to (eg 'pl_namespace')
* @param string $subKey Field name to match the sub-level keys to (eg 'pl_title')
* @return string|bool SQL fragment, or false if no items in array
* @param string $baseKey Field name to match the base-level keys to (eg 'pl_namespace')
* @param string $subKey Field name to match the sub-level keys to (eg 'pl_title')
* @return string|bool SQL fragment, or false if no items in array