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https://issues.apache.org/jira/browse/DERBY-1620?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12463050
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John Peterson commented on DERBY-1620:
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Yes, that comment isn't very clear. I was trying to remind the reader that the
SQLParser parses NULL's in the CASE expression into UntypedNullConstantNode's
and then casts those nodes into CHAR's. Thus the only situation in which the
case statement is returning a CHAR will this check need to be performed.
Ultimately to avoid having the NULL casted to a CHAR for a second time
(duplicate work). Thanks for pointing it out, I will have to clarify.
I was working on some test cases, but while writing them I realized that patch
I provided doesn't handle nested WHEN's. A rather severe oversight. So once
solution is to recursively examine "else" nodes to determine if they are
another conditional node. I have been delaying updating the code, however,
because it's not clear to me as to why Derby is casting NULL's into CHAR's in
the first place. This question of course begs a more detailed look into the
underlying Derby code than I have yet undergone. In fact, I am planning on
posing it to the Derby community, for I would be most interested in any
feedback.
> SQL CASE statement returns ERROR 42X89 when including NULL as a return value
> ----------------------------------------------------------------------------
>
> Key: DERBY-1620
> URL: https://issues.apache.org/jira/browse/DERBY-1620
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Affects Versions: 10.2.1.6
> Environment: Windows XP
> Reporter: John Peterson
> Assigned To: John Peterson
> Priority: Minor
> Attachments: ConditionalNode.diff, ConditionalNode_diff.txt,
> Derby_Community_Discussion.doc, derbyall_report.txt, sysinfo_and_example.txt
>
>
> This bug appears to be related to the DERBY-7 bug (NULLIF() function). When
> NULL is used during a CASE statement, Derby requires the NULL to be CAST to
> the appropriate type. This does not appear to meet the SQL 2003 Standard for
> the Case Expression (see attached Word document). See the attached Word
> document to view the Derby Community Discussion about this issue. See the
> attached .TXT to view the SYSINFO and to see an example of the steps to
> reproduce using IJ.
> Steps to Reproduce:
> ij>values case when 1=2 then 3 else NULL end;
> ERROR 42X89: Types 'INTEGER' and 'CHAR' are not type compatible. Neither
> type is assignable to the other type.
> Current Workaround:
> ij>values case when 1=2 then 3 else cast(NULL as INT) end;
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