Postgres 8.3 - type error when creating packages

to duplicate this, create an order and then go to fulfill it. (I was working through the examples in "Using Drupal" by Byron et. al. from O'Reilly). When you hit the "packages" tab, you get an error:

warning: pg_query() [function.pg-query]: Query failed: ERROR: type "unsigned" does not exist LINE 1: ...r_product_id, CAST(SUM(op.qty) / COUNT(pp.qty) AS UNSIGNED) ... ^ in /var/www/drupal-6.8/includes/database.pgsql.inc on line 139.

user warning: query: SELECT op.order_product_id, CAST(SUM(op.qty) / COUNT(pp.qty) AS UNSIGNED) AS total, SUM(pp.qty) AS packaged FROM uc_order_products AS op LEFT JOIN uc_packaged_products AS pp ON op.order_product_id = pp.order_product_id WHERE op.order_id = 1 AND op.data LIKE '%s:9:"shippable";s:1:"1";%' GROUP BY op.order_product_id HAVING SUM(pp.qty) IS NULL OR CAST(SUM(op.qty) / COUNT(pp.qty) AS INTEGER) > SUM(pp.qty) in /var/www/drupal-6.8/sites/all/modules/ubercart/shipping/uc_shipping/uc_shipping.admin.inc on line 48.

I tried changing casts to UNSIGNED to be casts to INTEGER, but then got a division by zero error. Looking at this further, the query doesn't make sense to me (divide the total number of items by the count of non-zero package values?), so I replaced the query on line 48 with :

$result = db_query("SELECT op.order_product_id
, SUM(op.qty) AS total
, SUM(pp.qty) AS packaged
FROM {uc_order_products} AS op
LEFT JOIN {uc_packaged_products} AS pp
ON op.order_product_id = pp.order_product_id
WHERE op.order_id = %d
AND op.data LIKE '%%%s%%'
GROUP BY op.order_product_id
HAVING SUM(pp.qty) IS NULL
OR CAST(SUM(op.qty) - SUM(pp.qty) AS INTEGER) >
SUM(pp.qty)", $order->order_id, 's:9:"shippable";s :1:"1";');

And this seems to work (it got me through the example in the book), but I really don't understand the semantics of what the query is trying to do.