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From "Bryan Pendleton (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3033) select query results in nullpointer exception in skipScan()
Date Fri, 31 Aug 2007 02:06:31 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3033?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12523980
] 

Bryan Pendleton commented on DERBY-3033:
----------------------------------------

Thanks Dag. This is an interesting line of code, and an interesting stack trace, particularly
given the observation that when the original reporter added an index, the problem went away.
I'm wondering if this problem is related to DERBY-2916 and DERBY-2775. 

Does the query in the bug involve an OUTER JOIN? or contain an IS [NOT] NULL condition? And
is this condition related to the index that was added which causes the problem to go away?

At the point where TableScanResultSet.openCore calls NoPutResultSetImpl.skipScan, there is
the following comment:

// Check whether there are any comparisons with unordered nulls
// on either the start or stop position.  If there are, we can
// (and must) skip the scan, because no rows can qualify

It seems like DERBY-2775 may have caused us to take some new paths through the code involving
"ordered null semantics", and the skipScan method is at the core of that code (see the DERBY-2916
comments for more discussion of this), so I have an intuition that this problem is related
to those changes.

For now, I'll link this issue to those issues, in the hope that my intuition is well-founded.

> select query results in nullpointer exception in skipScan()
> -----------------------------------------------------------
>
>                 Key: DERBY-3033
>                 URL: https://issues.apache.org/jira/browse/DERBY-3033
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.2.2.0
>         Environment: Windows XP, Java 5.0, JDBC, Derby 10.2.2.0
>            Reporter: Haolan Qin
>         Attachments: d3033-sane-ij-session-10.3.1.5.txt, test.rar
>
>
> The following error was repeatedly thrown when we tried to run a select query via JDBC.
Strangely, the exact same select query did not trigger any error when run from the command
line console. After we added an index, the error went away completely. 
> java.lang.NullPointerException
>  at org.apache.derby.impl.sql.execute.NoPutResultSetImpl.skipScan(Unknown Source)
>  at org.apache.derby.impl.sql.execute.TableScanResultSet.openCore(Unknown Source)
>  at org.apache.derby.impl.sql.execute.IndexRowToBaseRowResultSet.openCore(Unknown Source)
>  at org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.openCore(Unknown Source)
>  at org.apache.derby.impl.sql.execute.JoinResultSet.openRight(Unknown Source)
>  at org.apache.derby.impl.sql.execute.JoinResultSet.openCore(Unknown Source)
>  at org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.openCore(Unknown Source)
>  at org.apache.derby.impl.sql.execute.SortResultSet.openCore(Unknown Source)
>  at org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.openCore(Unknown Source)
>  at org.apache.derby.impl.sql.execute.BasicNoPutResultSetImpl.open(Unknown Source)
>  at org.apache.derby.impl.sql.GenericPreparedStatement.execute(Unknown Source)
>  at org.apache.derby.impl.jdbc.EmbedStatement.executeStatement(Unknown Source)
>  at org.apache.derby.impl.jdbc.EmbedPreparedStatement.executeStatement(Unknown Source)
>  at org.apache.derby.impl.jdbc.EmbedPreparedStatement.execute(Unknown Source)
>  at org.apache.derby.impl.drda.DRDAStatement.execute(Unknown Source)
>  at org.apache.derby.impl.drda.DRDAConnThread.processCommands(Unknown Source)
>  at org.apache.derby.impl.drda.DRDAConnThread.run(Unknown Source)

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