I'll leave it to others to explain why but it's sometimes faster to do an
outer join with a not null:
select whatever from table1, table2+
where table2.whatever is not null;
I've had selects of that form run in seconds where the sub-select or the
straight join form took hours.
"Carle,
William T To: Multiple recipients of list ORACLE-L
<[EMAIL PROTECTED]>
(Bill), cc:
ALCAS" Subject: Join vs. Subselect
<wcarle
@att.com>
Sent by: root
11/11/2002
11:23 AM
Please
respond to
ORACLE-L
Hi,
Here is the situation. The application coded a query that looks like
this:
select * from table1
where objid in (select objid from table2);
There is an index on objid in table 1 that isn't being used. An explain
shows it is using this system view vw_nso_1 that is used to transform an IN
subquery to a join. If you recode the query to:
select a.* from table1 a, table2 b
where a.objid = b.objid;
Then it will use the index. My question is: shouldn't it use the index
in both cases. I know the join is a better way to code it and I have told
the application that, but I would think that the first way would use an
index anyway. Ideas?
Bill Carle
AT&T
Database Administrator
816-995-3922
[EMAIL PROTECTED]
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