Re: Individual Indexes v.s. One "combinded" Index
Date: 13 Oct 1994 19:48:57 GMT
Message-ID: <37k2v9$i6n_at_fred.uswnvg.com>
: Oracle will pick ONE index and retrieve all rows that satisfy THAT single
: criteria AND then examine each identified row to exclude those that fail the
: other column criteria.
: This is the reason why it is best to have a concatenated index (or as unique
: as possible) that narrows down the candidate search rows very quickly.
: I have never seen Oracle do the multiple index scanning (on one table) and
: then sort-merge that you have detailed above.
: Bruce... pihlab_at_cbr.hhcs.gov.au
Correction to the above:
ORACLE DOES use multiple indexes (ie merging the indexes) that satisfy the criteria it uses. I know! I have seen it a few times in both "tkprof" and "explain". The key word is "the criteria it uses", NOT what YOU think! So, go back and read up on the performance tuning guide to find out more about those criteria and their order of importance.
Kim Ng
(Just a low life contract programmer. Thus, my clients won't adopt my views.) Received on Thu Oct 13 1994 - 20:48:57 CET