Questions like this question and this list seem to cover it reasonably well but our FAQ really doesn't cover when I should be asking a DBA and when I should be asking a programmer; on occasiona I've also been unsure whether a mostly/only SQL query question on StackOverflow should be migrated to here or not.
It seems to me that any question dependent on a programming language belongs clearly on SO, and that should be mentioned explicitly in the FAQ. When there's a finer line I wouldn't be able to say myself, such as when a programming problem is solely because of a misuse of SQL or database design, but I think our FAQ needs to be clear about that.
It looks like DBA.SE hasn't started customizing it's FAQ yet but IMO this would be one of the most important things to include, since it defines what questions are actually in our scope.