You'd think that the SQL-92, ODBC, and JDBC standards would make it reasonably easy to write programs that can work with many different RelationalDatabases. They help, but there's a long way to go. I'm starting this page to document differences between SQL databases as I find them. Hopefully it will turn into a useful resource.
Some portability issues to get started:
How about:
EditHint: Consider merging with DatabaseVendorLock, because this is small.
See Also RelationalLanguage, SqlFlaws, DatabaseVendorLock, QueryWrapperLanguageOverSql
[CategoryDatabase - relational DB discussion]