Target table post load command query Can we use a query joining two diff Data store tables

How to use query using two differenet tables from two datastores.using a join, is it possible.

Within the query how to reference table1 from datastore1 if it is possible can someone please provide syntax.

I want to use an update statement using a multi table join, part of two data stores. in Post load command.

Thanks a lot for the helpful info.