How to connect collections/tables by ID in order to get the values

Hi everyone!

So I've been trying this stuff for a while and I can't seem to get it or solve it. I'm using jqm.

I need to connect my collections/tables by ID. Just like we connect it using php like:
"SELECT * from collection1 as a, collection2 as b WHERE =;"

But I get confused when applying it on mapping.
Can anyone guide me how to do this please??

I have here a visual, if my explanation is confusing.

My main reason why I need this, is because I need to get a value from a collection using the query service I have in invoke event in another collection.

Thank you in advance!
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