Hello

Yep there is still nothing wrong with my explanation thats bcoz
the parameter

optimizer_mode can take on values

o RULE - always use RBO (unless the query is hinted or accesses
an object the RBO doesn't know about)

o CHOOSE - Use RBO if no stats are on any of the tables in a
query. Use CBO if any are analyzed (or there are
hints or accessing an object the RBO cannot)

o FIRST_ROWS - Optimize with the CBO. Try to get a plan tha
gets the first row of the result set the fastest

o ALL_ROWS - Optimizer using CBO. Try to get a plan that
gets the last row of the result set the fastest.


As to which value you should use -- it would be up to you.
There is no "best" value for all (if there was, we would have
but one setting)...

In general, CHOOSE is appropriate.

if you are on oracle 7.3 and above the cost based optimizer will use statistics if staistics are present unless you overide them in your sql statement.