PL/SQL is Oracle's proprietary extension to SQL. It is a very powerful Tool and essential skill for anyone who is a Oracle professional.
This Page contains a number of useful and relevant links.
Here's a Product Review from
from OraFAQs which provides a useful comparison of some leading Products,
a listing about 35 products provided by Bill Pribyl, author of O'Reilly's excellent
'Learning Oracle PL/SQL".