RE: Query performance question
- From: "Guang Mei" <GMei@xxxxxx>
- To: <mschmitt@xxxxxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 2 Mar 2006 17:27:27 -0500
try something like
select cnt from (
select count(*) cnt from fred.table_a A
where A.col_1 in (select col_3 from fred.table_b B where B.col_4 = '662')
Union
select count(*) cnt from fred.table_a A
where A.col_2 in (select col_3 from fas.table_b B where B.col_4 = '662');
Assume you have index on A.col_1, A.col_2, B.col_3, B.col_4
Guang
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]On
Behalf Of Mike Schmitt
Sent: Thursday, March 02, 2006 5:20 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: Query performance question
Hi All,
I was hoping someone could help me figure out a way to get better performance
from the following query. This is in a 10.2.0.1 instance with updated
statistics
This following query takes 6 minutes ~27million consistent gets:
select count(*) from fred.table_a A
where A.col_1 in (select col_3 from fred.table_b B where B.col_4 = '662')
or A.col_2 in (select col_3 from fas.table_b B where B.col_4 = '662')
If I make the above statement into two separate queries, each one takes
approximately 1 second.
for example:
1 second ~1400 consistent gets
select count(*) from fred.table_a A
where A.col_1 in (select col_3 from fred.table_b B where B.col_4 = '662')
..............................
I have tried using various hints, however my tracing keeps showing that the
statement with the 'or' continues to want to access table_A (which is ~7million
rows) with a full table scan. While the individual queries access table_A by
way of indexes on col_1 and col_2.
Any ideas on how I can get the optimizer to handle this query differently, and
get the timing more in line with the individual queries.
Thanks in advance
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