Sorry for the late response I often planned to write a reply but then forgot in my hurry. :-D
I use the database for queries which combine data from Reviewboard and from my other applications I use. I mentioned Polarion already, I use the Review Board tool to review work items which are stored in my Polarion. In the Summary of a review, the work item ID is visible and therefore I can apply a SQL Join on the the review_reviewsrequest table with the work items table and see at a glance, for which work items I have reviews and for which I have not.
You may wonder how it can work to make combined queries with an MySQL source (Reviewboard) and a PostgreSQL source (Polarion), for this I use the Microsoft SQL Server Management Studio.
There I can indclude the database of the applications I use as Linked Servers and mix SQL Server queries with MySQL and PostgreSQL queries with the
OPNEQUERY function.
You see, in this case the API is not an option. ;-)
Best regards