Expression rule for multiple table

In your conceptual model you need to separate the data model aspect from the data retrieval aspect. Expressions can retrieve data from a "data model" but not (easily) implement such a model.

In your example you have two choices:

1. create two different Record Types, one for Order and one for Customer, and then have Orders nested as a multiple under Customer. You can then use a!queryRecordType() to retrieve the data
2. create a database VIEW which joins the data as you describe, then create a CDT from the VIEW and then an expression that contains a a!queryEntity() that retrieves data from that VIEW

Note that 1., is essentially Appian's way of effectively implementing 2. without having to resort to creating database VIEWs.

Hi there,

Stewart Burchell has already told you the two ways. Another approach can be to query 2 different tables by passing the output of one QE into another as input and then combining the result in a third expression rule. However, I would still prefer creating records and then using record relationships. 

Yes, I inferred this was possible, but it's not an easy option and, frankly, why would you opt for this when there are much easier options available to you.

I agree.