RE: Query performance question

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_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org]On Behalf Of Mike Schmitt Sent: Thursday, March 02, 2006 5:20 PM
To: oracle-l_at_freelists.org
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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http://www.freelists.org/webpage/oracle-l Received on Thu Mar 02 2006 - 16:27:27 CST