kk, did realize it was that resource intensive...

what about a tracking table that is updated via a trigger that is executed only if a country has an active standing order on the market and their cash on hand changes.

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country id | resource | ask price | ask qty | cash on hand | active | buy power
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update the ask price, ask qty, cash on hand, active and buy power when those change.

buy power = cash on hand / ask price

Deactivate any standing order when buy power = 0 or when ask qty = 0.