Re: ODBC connection - extra statements being run

Morning John,

Norman Dunbar.
Contract Oracle DBA.
Rivers House, Leeds.

Internal : 7 28 2051
External : 0113 231 2051

>>> "Fedock, John (KAM.RHQ)" <John.Fedock_at_us.kline.com> 02/08/06 08:46pm >>>
>> When a user connects to my HP-UX 10g database from Excel via ODBC
and runs a SQL select statement joining 2 tables, a 10046 trace clearly shows >>that statement running quickly, then another mysterious statement running, which is basically a select from the 2 tables with no join. This causes it to >> run for more than 10 minutes. The original statement runs < 2 second in SQLPLUS. Can anyone explain?

I had a similar problem, without the mysterious query though, using ODBC from Access to Oracle.

The access query did the equivalent of :

SELECT stuff
FROM table_a, table_b, table_c
WHERE table_a.something contains "some text" AND <other joins here>;

ODBC fiddled about and discovered that the column being searched was a LONG in the database. I presume it figured out that you cannot do a LIKE on a LONG in Oracle so it simply dropped the where clauses off and pulled back a cartesian join of all three tables in the query. I presume the intention was to do some sort of filtering out at the Access end rather than on the big, powerful, Oracle server end.

Unfortunately, the three tables were three of the biggest in the database and a three way cartesian join resulted in something like 27 thousand million billion rows being 'returned' to Access. The cost of the statement was something like 2567 G in the explain plan. The Access user decided that the response time was too long and closed Access down. This left the query still running at the Oracle end.

After a week and a half running (honest) Oracle started to sort the results and the box simply stopped - the TEMP space was being absolutely hammered.

My advice is simple :

"ODBC - just say NO!"

HTH Cheers,
Norm.

Information in this message may be confidential and may be legally privileged. If you have received this message by mistake, please notify the sender immediately, delete it and do not copy it to anyone else.

We have checked this email and its attachments for viruses. But you should still check any attachment before opening it.

We may have to make this message and any reply to it public if asked to under the Freedom of Information Act, Data Protection Act or for litigation. Email messages and attachments sent to or from any Environment Agency address may also be accessed by someone other than the sender or recipient, for business purposes.

If we have sent you information and you wish to use it please read our terms and conditions which you can get by calling us on 08708 506 506. Find out more about the Environment Agency at www.environment-agency.gov.uk

--
http://www.freelists.org/webpage/oracle-l