>"Not waving them away, just saying that these kinds of issues are not all that common because most real-world databases are trivial cases." If this is the cas

>"Not waving them away, just saying that these kinds of issues are not all that common because most real-world databases are trivial cases." If this is the case, then, it's only because database application developers go out of their way to write compatible code. Things like upserts are not trivially compatible between vendors, and so are avoided by people trying to write portable applications. Similarly, let's look at SQL 2003 structure data type inheritance and how this is implemented in Informix, Oracle, DB2, and PostgreSQL. Ok, so it isn't in PostgreSQL, and Informix allows tables to be inherited as well as types, and will even happily return result sets with different numbers of columns per row (google "Informix jagged rows")... And Oracle and DB2 look pretty close in this way until you get under the hood.