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From "Bryan Pendleton (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-2459) Ordering on a CASE-expression casues a NullPointerException when using a UNION
Date Wed, 23 May 2007 21:20:16 GMT

    [ https://issues.apache.org/jira/browse/DERBY-2459?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12498378
] 

Bryan Pendleton commented on DERBY-2459:
----------------------------------------

In the problem description, the CASE expression in the ORDER BY clause
is identical to the CASE expression in each of the SELECT statements in
the child table expressions of the UNION.

The problem also occurs even if the CASE expression in the ORDER BY clause
is unique: for example, replacing the ORDER BY clause in the description by
  order by CASE WHEN t2.value IS NOT NULL THEN t1.id ELSE t1.ref END
still results in the NPE.


> Ordering on a CASE-expression casues a NullPointerException when using a UNION
> ------------------------------------------------------------------------------
>
>                 Key: DERBY-2459
>                 URL: https://issues.apache.org/jira/browse/DERBY-2459
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.1.3.1, 10.1.3.2, 10.2.1.6, 10.2.2.0, 10.2.2.1, 10.3.0.0
>         Environment: Java 1.5.0_06-b05 on Linux Ubuntu 5.10. Derby version 10.2.2
>            Reporter: Lars Gråmark
>         Assigned To: Bryan Pendleton
>
> When an order by clause involves a CASE-expression as seen below, a NullPointerException
is thrown. The error only occurs when two select statements are combined in a union (or union
all).
> select t1.id, CASE WHEN t2.value IS NOT NULL THEN t2.value ELSE t1.value END
> from A1 t1
> left outer join B1 t2 ON t2.id = t1.ref
> union all
> select t1.id, CASE WHEN t2.value IS NOT NULL THEN t2.value ELSE t1.value END
> from A2 t1
> left outer join B2 t2 ON t2.id = t1.ref
> order by CASE WHEN t2.value IS NOT NULL THEN t2.value ELSE t1.value END
> --Use the following statement to reproduce the problem:
> create table A1
> (
>    id char(1)
>   ,value int
>   ,ref char(1)
> );
> create table A2
> (
>    id char(1)
>   ,value int
>   ,ref char(1)
> );
> create table B1
> (
>    id char(1)
>   ,value int
> );
> create table B2
> (
>    id char(1)
>   ,value int
> );
> insert into A1 (id, value, ref) values ('a', 12, 'e');
> insert into A1 (id, value, ref) values ('b', 1, null);
> insert into A2 (id, value, ref) values ('c', 3, 'g');
> insert into A2 (id, value, ref) values ('d', 8, null);
> insert into B1 (id, value) values ('e', 4);
> insert into B1 (id, value) values ('f', 2);
> insert into B2 (id, value) values ('g', 5);

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