allow system to use 2 different access paths for 2 different columns in a
select list.
--------------------------------------------------------------------------------------
Key: DERBY-886
URL: http://issues.apache.org/jira/browse/DERBY-886
Project: Derby
Type: Improvement
Components: SQL
Reporter: Mike Matrigali
Priority: Minor
"SELECT MIN(Id) FROM Customer" and "SELECT MAX(Id) FROM Customer" are both
fast, but "SELECT MIN(Id), MAX(Id) FROM Customer" is slow, taking 5 seconds.
Derby knows how to use an index to quickly find a minimum or a maximum (by
traversing down one side of the B-tree or the other). It doesn't know how to do
both in the same query, which would take two traversals. There may be a few
other cases in Derby where special access paths are used to return function
results (I think there is some magic for finding if a null exists, but not
sure).
Some notes from discussion on the development list:
>
> Is the work to fix this the same as making IN list use multiple probes,
> and/or makeing OR lists do multiple probes? There are existing JIRA
> items for those, or is it different enough to have a separate JIRA?
I believe they're different. While each case would use multiple probes, in the
MIN/MAX case one of the probes would go down the right side of the BTree, while
in the IN/OR case it would do "normal" scans. Also, the MIN/MAX case and the
IN/OR case would require different logic to recognize when the optimizations
are possible. The costing logic in the optimizer would be different, too. It's
possible the two cases could share some execution code, but the rest of it
would require different implementations.
--
This message is automatically generated by JIRA.
-
If you think it was sent incorrectly contact one of the administrators:
http://issues.apache.org/jira/secure/Administrators.jspa
-
For more information on JIRA, see:
http://www.atlassian.com/software/jira
