RE: Strategies for dealing with (NOT EQUAL) conditions and indexes
- From: "Mark W. Farnham" <mwf@xxxxxxxx>
- To: <mwf@xxxxxxxx>, <ChrisDavid.Taylor@xxxxxxxxxxxxxxx>, "'Stephens, Chris'" <Chris.Stephens@xxxxxxx>
- Date: Thu, 17 Nov 2011 09:00:57 -0500
Argh. I sent that carefully formatted to not wrap and be proportional, but
apparently the mail chain stripped all that off and wrapped the heck out of
it.
This:
select --+ gather_plan_statistics a,d from junk13 where (a < '1' or a >'1')
and d != 'not aA'
was the key point.
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]
On Behalf Of Mark W. Farnham
Sent: Thursday, November 17, 2011 8:54 AM
To: ChrisDavid.Taylor@xxxxxxxxxxxxxxx; 'Stephens, Chris'
Cc: oracle-l@xxxxxxxxxxxxx
Subject: RE: Strategies for dealing with (NOT EQUAL) conditions and indexes
Okay, I did not realize the not equals was on the indexed column rather than
the non-indexed column.
In the following, there is an index on columns (a,b,c), and none on d. But a
is highly selective (one row in fact, since I didn't want to fool around and
find the break point).
The value on D is then just filtered out from the one row the index returns.
So if the costs are right, you can turn a single not equals into the
concatenation of a pair of index range scans with a table probe
instead of a fast full index scan or a full table scan.
<snip>
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