Make sure to checkout the Microsoft Dynamics GP 2015 R2 – Purchasing All-in-One View
Microsoft Dynamics GP 2015 R2 – Purchasing All-in-One View – Microsoft Dynamics GP Community
Sales, Purchasing & InventorySQL & DataMicrosoft & the GP EcosystemGP 2015
Archived post from 2015. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.