Those who will to stay in 9.2 for a long time :-( ; anybody has noticed if Oracle will at some point backport some cbqt funcionality to 9.2.0.8? (plead for costing unnesting at least)

The modified query looks like an option that the 10g optimizer would have investigated as a viable rewrite of the original query; so in principle I see no reason why it shouldn’t end up as the query sent to the 9i instance.

I have seen a peculiar issue. Infact, I will say that I have not seen this but have heard from one of my fellow dba. One of the query executed on 10.2.0.1 fetches the data from 9206 using db link. The Query executed on 10.2.0.1 when goes to 9206, the query text changes. I understand that the Query is internally rewritten only to check and understand the execution plan (comple view merging etc.) but v$sqlarea will report the original statement executed. In this case, the Query X changes to Y. The query is similar to the pasted below :

Query Executed from 10.2.0.1

select e.empno, e.ename, d.dname, e.sal
from emp@o9i e, dept@o9i d
where e.deptno = d.deptno
and e.sal = (select max(ep.sal) from emp@o9i ep where ep.deptno = d.deptno)

Query seen on 9206

select a1.empno, a1.ename, a3.dname, a1.sal
from (select max(sal) sal, deptno from emp group by deptno) a2,
emp a1, dept a3
where a1.deptno = a3.deptno
and a1.sal = a2.sal
and a3.deptno = a2.deptno

Both the query fetch the same output, but since, the emp table is huge, the second query takes time to execute. Can Oracle Optimizer rewrite the query and change the entire text ?

I tried to simulate this and could not find this to be true. The alias name etc. are changed as a1, a2 etc when the query is executed from 10g and passed on to 9i.

Regards

http://delivery.acm.org/10.1145/1170000/1164215/p1026-ahmed.pdf?key1=1164215&key2=7529733711&coll=&dl=ACM&CFID=15151515&CFTOKEN=6184618

Thanks,
Anurag