Join / Read Data

How do I join in additional data to be displayed in a drop-down that is fed by a read data?
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Please see the belowimage. The data being displayed there is coming from a read data that is using a CONCAT statement. I'd like to display the trainer's name instead of the ID number, but the name is in another table. Can you help please? Thanks!
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There's an "add model" button on the read data action. And the format will be
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CONCAT(model.fieldname , ' | ' , model.otherfieldname , ' | ' , model.otherotherfieldname):model.alias
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Take note of the space around each comma

Oh nice, thanks. Thank you for the note on the comma, that explains some past difficulties. I had to setup like this for my situation. (used the relation conditions)
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