multi table subscription

it would be nice to be able to write subscriptions that subscribe to multiple tables at once with conditions that link them. something like:

"SELECT * FROM auction_listing as AL, user_name as UN, item_lookup as IL WHERE AL.cathegory = 'Weapon' LINK AL.entity_id = UN.entity_id, AL.item_id = IL.item_id"

and it is like writing 3+ separate subscriptions and returns the rows of the 3 tables where the link and where condition matches.
the problem currently is that it is a pain to get related data from multiple tables without opening potentially hundreds to thousands of subcriptions per client.