DB & MDB2 Portability

I have recently started porting one of our (very) large applications from PHP4 + DB to PHP5 + MDB2. My question is as follows: In the PHP4 version, we used MySQL as the primary RDBMS, but in the PHP5 version would like to give the user the option to use Postgres, Oracle and MSSQL as well. As far as I can see, things should all be OK with the different backends, but for one question. Can MDB2 abstract the column types and names properly? I see that there is support for datetime columns, but not some others, like timestamp, null fields (for Oracle), booleans, CLOB's, Decimals, etc. I have looked at an object by Daniel Convissor that does this type of abstraction correctly, for all of the above quirks (and more). Am I flogging a dead horse by implementing this as a separate layer in my db abstraction? or is it still necessary? I have googled for information around this point, but can't find anything satisfactory. I have also tried looking through the API docs for MDB2 as well as the code, but could only find a couple of references to portability, namely in the terms described above. Could anyone either confirm or deny my findings? I would hate to carry on re-inventing the wheel if its not useful! Any pointers would be a great help! --Paul