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https://issues.apache.org/jira/browse/DERBY-2998?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12575788#action_12575788
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A B commented on DERBY-2998:
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> I do not have any more work lined up on this for 10.4.
Okay, thanks Thomas!
The reason I asked is because on Feb 25 I posted a bunch of comments, of which
#8 mentioned how predicates on a ROW_NUMBER() do *not* actually limit rows from
store, and thus such a restriction will probably not meet the performance
expectations of the user who specifies it. For reference, the example query
was:
SELECT * FROM (
SELECT row_number() over () as r, t.* FROM T
) AS tmp WHERE r <= 3;
for which the plan shows the following for the top-most
ProjectRestrictResultSet:
******* Project-Restrict ResultSet (1):
Number of opens = 1
Rows seen = 1280
Rows filtered = 1277
restriction = true
So we actually read all 1280 rows from disk, then filtered 1277 of them out so
that, in the end, we only returned 3 rows.
In response to that you wrote (on Feb 26):
Thomas> It seems we don't take the fact that we know we have an ascending column
Thomas> into consideration any more (we used to). I'll have to have another
look at this.
So is it safe to say that this will *not* be addressed for 10.4? That's
perfectly fine, I just want to make sure we're clear on that (esp. so that if
users ask, we can give a clear answer :) Do you think it would be worth it to
file a separate enhancement Jira for that particular task? (or is there one
already?)
> Add support for ROW_NUMBER() window function
> --------------------------------------------
>
> Key: DERBY-2998
> URL: https://issues.apache.org/jira/browse/DERBY-2998
> Project: Derby
> Issue Type: Sub-task
> Components: SQL
> Reporter: Thomas Nielsen
> Assignee: Thomas Nielsen
> Priority: Minor
> Attachments: d2998-10.diff, d2998-10.stat, d2998-11.diff,
> d2998-12.diff, d2998-12.stat, d2998-13.diff, d2998-13.stat, d2998-14.diff,
> d2998-14.stat, d2998-15.diff, d2998-15.stat, d2998-16.diff, d2998-16.stat,
> d2998-17.diff, d2998-17.stat, d2998-18.diff, d2998-18.stat, d2998-19.diff,
> d2998-19.stat, d2998-4.diff, d2998-4.stat, d2998-5.diff, d2998-5.stat,
> d2998-6.diff, d2998-6.stat, d2998-7.diff, d2998-7.stat, d2998-8.diff,
> d2998-8.stat, d2998-9-derby.log, d2998-9.diff, d2998-9.stat,
> d2998-doc-1.diff, d2998-doc-1.stat, d2998-doc-2.diff, d2998-doc-2.stat,
> d2998-followup-2.diff, d2998-followup-2.stat, d2998-followup-distinct.diff,
> d2998-followup-distinct.diff, d2998-followup-distinct.stat,
> d2998-followup-doc3.diff, d2998-followup-doc3.stat,
> d2998-followup-issue1.diff, d2998-followup-issue1.stat,
> d2998-followup-issue4.diff, d2998-followup-issue4.stat,
> d2998-followup-removeunused.diff, d2998-followup-testsuite.diff,
> d2998-followup-testsuite.stat, d2998-test.diff, d2998-test.stat,
> d2998-test2.diff, d2998-test2.stat, d2998-test3.diff, d2998-test3.stat,
> d2998-test4.diff, d2998-test4.stat, d2998-test6.diff, d2998-test7.diff,
> d2998-test8.diff, d2998-test9.diff, rreffuncrownumber.html
>
>
> As part of implementing the overall OLAP Operations features of SQL
> (DERBY-581), implement the ROW_NUMBER() window function.
> More information about this feature is available at
> http://wiki.apache.org/db-derby/OLAPRowNumber
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