Reverse engineering complex join queries

We study the following problem: Given a database D with schema G and an output table Out, compute a join query Q that generates OUT from D. A simpler variant allows Q to return a superset of Out. This problem has numerous applications, both by itself, and as a building block for other problems. Related prior work imposes conditions on the structure of Q which are not always consistent with the application, but simplify computation. We discuss several natural SQL queries that do not satisfy these conditions and cannot be discovered by prior work.