Usually when i need to compare data from two tables without wanting to join them do i normally use mapping load. which creates a temporary table that can be referenced and give you additional data or instance item cost.
it could look something like this:
In the load statement where you need additional data would i call for that temporary table and will be able to insert additional data based on a field value that is matched.
applymap('Map_Table,ItemNo) as ItemCost, //this will give you the cost for every itemNo.
Might be worth a try?
Peek function is also an inter record function that is used for the similar purpose: http://help.qlik.com/sense/2.1/en-US/online/#../Subsystems/Hub/Content/Scripting/InterRecordFunctions/Peek.htm?Highlight…
May be with a sample of your 2 tables , or directly a .qvf , il would be easier to bring advise.
Nethertheless for my opinion i would load the 2 tables a tempdate, then join the 2 tables in only one so that i can add a calculated dimension with an IF statement for new calculation.
have a look to this link maybe :
Or search in the forum with those keyword : "join table for calculation"
Hope it helps