We found a bug in some old code. And we fixed it. Then other stuff started failing. It turned out that there were some other code, using the same function, that worked because of the bug. That forced us to roll back the fix and thereby re-introduce the initial bug that weren’t as critical.
So – we had to find a way to find out which code-paths were working because of the bug so we could fix those.
I had a task to clean up some data and I decided to use in-database archiving, a new feature in 12c. As I was working I noticed some unexpected resultsets along the way. I was quite puzzled for a little time, so I set up a test-case and realized that I’ve struck on a bug. The bug seems related to the ANSI re-architecture-features of the optimizer.