Are you already familiar with RDBMS concepts and SQL? This will determine how introductory the book has to be.<br>
<br>
For third party books, you might try Oracle8: A Beginners Guide or Oracle8: The Complete Reference (horribly misnamed!). Both are from Oracle Press.<br>
<br>
If you are already familiar with RDBMS in general, I recommend the Server Concepts Guide that comes as part of the Oracle documentation suite.