Oralce

You can visit here for the OLAP question:
http://forums.oracle.com/forums/thread.jspa?threadID=519250&tstart=45

Secondly, you should visit here:
http://www.oracle.com/technology/documentation/index.html

Remember this is what I have learned read+practice. The more you read the better and practice as much as you can.

You can also visit for interviews:
http://www.dba-oracle.com/bp/bp_book2_jobs.htm
http://forums.oracle.com/forums/thread.jspa?messageID=1888990&#1888990
http://forums.oracle.com/forums/thread.jspa?messageID=1859100&#1859100
Here is my list of DBA job skills:

http://www.dba-oracle.com/oracle_tips_dba_job_skills.htm

Here are notes on becoming a DBA:

http://www.dba-oracle.com/t_how_to_become_an_oracle_dba.htm