Re: indexing "select" columns

A copy of this was sent to lrzhemov_at_home.com (Leon) (if that email address didn't require changing) On 4 Jun 2001 13:32:09 -0700, you wrote:

>I hope Oracle would use only index to select information from the
>table as soon as all information is present in an index, so
> select col2
> from table1
> where col1= value
>would use only index as soon as index
>CREATE UNIQUE INDEX12 ON table1(COL1, COL2)
>exists
>Unfortunately statistics for select like that shows that speed of this
>query is exactly the same as with index "CREATE UNIQUE INDEX1 ON
>table1(COL1)"
>
>Does anybody has good experience in using "index only" (simulating
>IOT) queries?
>Potentially it should be faster then IOT as soon as indexes could be
>cached in memory but IOT can't.
>
>Thanks
>Leon

See
http://asktom.oracle.com/pls/ask/f?p=4950:8:::::F4950_P8_DISPLAYID:748446466563

Examples showing the performance differences possible are there.

--
Thomas Kyte (tkyte_at_us.oracle.com) Oracle Service Industries
Howtos and such: http://asktom.oracle.com/ http://asktom.oracle.com/~tkyte/
Oracle Magazine: http://www.oracle.com/oramag
Opinions are mine and do not necessarily reflect those of Oracle Corp