Query problem.

I am using Sybase Adaptive Server Anywhere (ASA) formally SQL Server Anywhere as a back end. I need to create a query or a stored procedure (whatever is more feasible) to get a result set based on several criteria. Let me set this up a bit. ASA uses TSQL so it is very similar.

Site table: This is a header table of all the locations that products will be delivered to.
SortCode table: This is a header table for product calsification
SampleFrequency table: Stores a matrix of sortcodes and sites to tell the system how often to mark a load for sampling.

My problem is the user wants to be able to put an entry of * in either the site number or sort code to make that frequency available to any sort code or site that has not been explicitly entered. For example:

Sites
1	Site number one
2	Site number two 

SortCodes:
A 		Sort A
B 		Sort B
C		Sort C

SampleFrequency  
Site		Sortno		Frequency
1		A		20%
*		*		100%

In the example above, if the user chooses site 1 sort A then the system would use a 20% sample. Otherwise, any other combination of choices would require a 100% sample. It seems to me that I should be able to do this with a couple of unions but I am having problem making it work.

Any help would be greatly appreciated.