Well, since Oracle does not deign to speak very standard-compliant SQL, a lot of Moodle code fails the first time on Oracle, until someone has actually tried it, and tweaked the queries that need tweaking.
If you turn on Debugging you should be able to find out what is failing. Then, perhaps with the help of some of the sql_xxx functions in lib/dmllib.php and the rules about AS at Development:XMLDB_problems#Table_and_column_aliases_-_the_AS_keyword, you may be able to fix it, or, at least, put high-quality bug reports in the Tracker.