When creating an epicor Origin, you must supply your username, password, Epicor API URL, and then choose a Service. The Epicor API URL will look like: https://starfish.epicorhosting.com/EpicorERPCTS/api/v1
The Service you select will look like ERP.BO.QuoteSvc or Ice.BO.DynamicQuerySvc. Each service contains a number of tables of data. You can only join between tables in the same Service. For example, if you are using the ERP.BO.QuoteSvc, you can join the Quotes and QuoteCnts tables:
SELECT * FROM Quotes left join QuoteCnts on Quotes.Company = QuoteCnts.Company and Quotes.QuoteNum = QuoteCnts.QuoteNum and QuoteCnts.PrimeContact = True
If you need to create custom SQL queries, you will have to use the Ice.BO.DynamicQuerySvc. You have to create the Query in Epicor, https://www.youtube.com/watch?v=xyTYoftHIYk, and then call that query with the Ice.BO.DynamicQuerySvc. If you need help with this, please email email@example.com.