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From "Bryan Pendleton (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-4406) Wrong order when using ORDER BY on non-deterministic function
Date Thu, 15 Apr 2010 00:57:49 GMT

    [ https://issues.apache.org/jira/browse/DERBY-4406?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12857165#action_12857165

Bryan Pendleton commented on DERBY-4406:

Sanity manager assertions are used to check situations that we believe
should never occur. They are placed in the code by programmers to
try to catch "impossible" situations. The assertions typically try to
give a more helpful error message about a problem in the data structures,
instead of the NullPointerAssertion or IndexOutOfRangeError that might
occur without the assertion.

If the code is changed, in such a way that the assertion no longer holds,
then it is completely reasonable to remove the assertion.

In this case, if your changes mean that it is no longer necessary to
require that the addedColumnOffset is non-negative, then your patch
should remove the assertion.

> Wrong order when using ORDER BY on non-deterministic function
> -------------------------------------------------------------
>                 Key: DERBY-4406
>                 URL: https://issues.apache.org/jira/browse/DERBY-4406
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions:,
>            Reporter: Knut Anders Hatlen
>            Assignee: C.S. Nirmal J. Fernando
> If I read the SQL standard correctly, a statement such as "select random() as r from
t order by random()" should be treated as "select random() as r from t order by r". Derby
does however generate a second, hidden random() column by which the rows are ordered.
> ij> create table t(x int);
> 0 rows inserted/updated/deleted
> ij> insert into t values 1,2,3,4,5;
> 5 rows inserted/updated/deleted
> ij> -- wrong result, not ordered by r
> ij> select random() as r from t order by random();
> R                     
> ----------------------
> 0.1285512465366495    
> 0.5116860880915798    
> 0.21060042130229073   
> 0.2506706923680875    
> 0.6378857329935494    
> 5 rows selected
> ij> -- correct result, ordered by r
> ij> select random() as r from t order by r;
> R                     
> ----------------------
> 0.0749025910679918    
> 0.07694931688380491   
> 0.1724114605785414    
> 0.2268758969382877    
> 0.31900450349277965   
> 5 rows selected

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