difference between oracle 9i and 11gr2 ?

The upgrade from 9i to 10g was significant, with many changes in the product itself, in the RMAN utility, in the Enterprise Manger; everything. The move from 10g to 11g was not as major, but there are some important differences. What I'm saying is that there is not enough space in this forum for a list of bullet points highlighting the things you will need to learn, and many of them may not be factors in what you have to know in the new position anyway. Since this is not a DBA position, you will probably not have to deal with the huge changes in Enterprise Manager and RMAN, or the deprecation of imp/exp in favor of Data Pump. However, there was a change in the default sort order when a GROUP BY clause has no explicit ORDER BY clause that occurred between two dot releases in 10g; you will be reverting to before that time and may encounter some unexpected bahavior.

I work primarily as a DBA and feel that the biggest changes have taken place at the architecture and utilities level, but that is not to say that nothing has changed in the PL/SQL arena. In my opinion, if you are a competent developer and comfortable with Oracle in general, then you should be able to at least get started in a 9i environment. Just get a good book (or bookmark a link) to a 9i SQL reference and be prepared to find that statements or syntax that you have been using for the past two years to behave differently or to not be there at all.

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