Here you go. I was in the car when I responded earlier.
“It’s not right for every situation, but several years ago I worked on a project with two separate code bases with recurring subscription systems. Due to a dispute with one of them and some limitations in services, we had to quickly request for every single user to manually update their subscriptions from one platform to the other. In order to make it as easy as possible, the new system needed to be able to know everything about the subscription on the old system so that users would only need to update their payment information and click a button. Our choices were to build an entire API on the old system with a legacy code base that nobody understood or to let the new database connect to the legacy database directly to perform joins. We ended up going with the second option and had a working version in production under two weeks with no issues. Everyone migrated successfully and the crisis was averted. Sometimes SQL is the best API.”
