Re: Multiple Indexes

Oracle can use multiple indexes. In the EXPLAIN PLAN output, this is identified by the AND-EQUAL operation.

I think your where clause must specify an equal condition for the full key of each index.

cyberkid_at_my-dejanews.com wrote:

> I have read that multiple indexes on one table cannot be used in combination
> on most RDBMS products. If there are multiple indexes, then the optimizer
> uses the best one, does a disk I/O to retrieve those records, and then goes
> through a full scan of those returned to match the remaining WHERE criteria.
> I've read elsewhere that the matched index pointers are compared, and THEN
> the records are retrieved. Which is correct? I'm looking at a 90 million
> record DB which will only be updated once every 3 months, and query
> performance is my key issue. Are there any good resources out there to find
> out exactly what methodology is used by Oracle, or other RDBMS's? Also, I've
> seen a product by DISC (Dynamic Information Systems Corp.) called Omnidex
> which uses "Inverted List Indexes" and "Dynamic Aggregation Indexes". Are
> these really better than typical B tree indexes? Surely there must be a
> trade off if they do perform better.
>
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Received on Wed Aug 26 1998 - 16:08:57 CDT