Olfgang, Thanks for the response. It was pointed out to me that my initial query and results were incorrect and I did resend the corrected query and results. Here too is the informaiton about the data in this particular column. SQL> select count (*) from aradmin.t185; COUNT(*) ---------- 41586 SQL> select count(unique(c1)) from aradmin.t185; COUNT(UNIQUE(C1)) ----------------- 41586 SQL> select c1,count(*) from aradmin.t185 2 group by c1 having count(c1) > 1; no rows selected Thank you. Bill Wagman Univ. of California at Davis IET Campus Data Center wjwagman@xxxxxxxxxxx (530) 754-6208 -----Original Message----- From: Wolfgang Breitling [mailto:breitliw@xxxxxxxxxxxxx] Sent: Thursday, December 21, 2006 10:58 AM To: William Wagman Cc: oracle-l@xxxxxxxxxxxxx Subject: Re: Why isn't Oracle Using My Index At 10:49 AM 12/21/2006, William Wagman wrote: >Greetings, > >This is a question I have been looking at and puzzling over for a couple >of days and am unable to explain, I'm hoping someone can help me >understand what is going on. In a 9i database I have a table with 41550 >rows on which stistics are generated weekly. In looking at a simple >select the query does not use an index and I am unable to figure out how >to make it use the index. > >SQL> set autotrace traceonly explain; >SQL> SELECT C240000008 FROM aradmin.t185 WHERE C1 = 'HD0000000041608' > 2 / > >Execution Plan >---------------------------------------------------------- > 0 SELECT STATEMENT Optimizer=CHOOSE (Cost=1420 Card=413 Bytes= > 627760) > > 1 0 TABLE ACCESS (FULL) OF 'T185' (Cost=1420 Card=413 Bytes=62 > 7760) > >There is an index IT185 on column C1 and column C1 is unique. A hint >will force the use of the index but in that this is not a locally >developed application I am unable to change the code. Nevertheless, in >attempting to understand this I looked at the clustering factor for the >index. You say c1 is unique. Oracle and the index stats don't seem to know that. How can you have avg_leaf_blocks_per_key > 1 for an index on a unique column? Regards Wolfgang Breitling Centrex Consulting Corporation www.centrexcc.com -- //www.freelists.org/webpage/oracle-l