Good Oracle resource are : any book written by Thomas Kyte or by any member of the "Oak Table".
As stated by T.Kyte : Read the Oracle concept guide from cover to cover, if you just retain 10% of what you've read, you will know more than 90% of the claimed "Oracle DBA".
also asktom web site + metalink + oracle website.
Oracle Database Online Documentation 11g Release 2 (11.2)
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By the way, i don't see the use of buying a book since the most up to date documentation about oracle is available online and for free ... the point is : taking the time to read & understand it