How to create a datasource to a combobox?

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Hi all!

I need do create a combobox just with related rows, and they are in a third
table.


Explaining better: I have a table of salesmen, another of customers and
another one with relationship of salesmen X customers. When I select a
salesman, I want only to show the customers that are related to him.

Does it have a way to create one datatable with the customers related to the
salesman to be used in the datasource of the combobox?

Thank you in advance,
Vanessa