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From "Mike Matrigali (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-4339) improve sort avoidance algorithm to include equijoin relationships
Date Wed, 05 Aug 2009 22:31:14 GMT

     [ https://issues.apache.org/jira/browse/DERBY-4339?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Mike Matrigali updated DERBY-4339:
----------------------------------


Here is another example of a query that could do sort avoidance with added code properly taking
into acount equijoin relationships:

select * from TENKTUP1, TENKTUP2
where TENKTUP1.unique1 = TENKTUP2.unique1
order by TENKTUP1.unique1 = TENKTUP2.unique1

The optimizer could pick either TENKTUP1.unique1 or TENKTUP2.unique1 as the outermost
node and then because it knows that TENKTUP1.unique1 = TENKTUP2.unique1 it would know
that the query also satisfies order by TENKTUP1.unique1 = TENKTUP2.unique1 without doing
an additional sort.  



> improve sort avoidance algorithm to include equijoin relationships
> ------------------------------------------------------------------
>
>                 Key: DERBY-4339
>                 URL: https://issues.apache.org/jira/browse/DERBY-4339
>             Project: Derby
>          Issue Type: Improvement
>          Components: SQL
>            Reporter: Mike Matrigali
>            Priority: Minor
>
> Not all sort avoidance paths are recognized by the optimizer.  Here is an example of
the class targeted by this issue, from 
> the wisc tests :
> select * from --DERBY-PROPERTIES joinOrder=FIXED
> TENKTUP2, TENKTUP1
> where TENKTUP1.unique1 = TENKTUP2.unique1
> and TENKTUP2.unique1 < 2500
> order by TENKTUP1.unique1';
> There is a unique index on TENKTUP1.unique1 and TENKTUP2.unique1.  To exercise the path,
the plan
> forces  TENKTUP2 as outermost join, knows that query result is sorted on TENKTUP2.unique1,
but does not
> recognize that because "TENKTUP1.unique1 = TENKTUP2.unique1" that query is also sorted
on TENKTUP1.unique1 and could avoid a sort.
> Note without the fixed join order a sort avoidance plan is picked by choosing the plan
where TENKTUP1.unique1 is the
> outermost node.

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