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From "A B (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3033) select query results in nullpointer exception in skipScan()
Date Wed, 12 Sep 2007 16:34:32 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3033?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12526843
] 

A B commented on DERBY-3033:
----------------------------

Hi Kathey,

My guess (and it's just a guess) is that, while startPosition itself may be null, it probably
is not correct for a non-null startPosition to have startPosition[i] be null for any i.

For what it's worth: startPosition in the above code comes from TableScanResultSet.startPosition,
which is in turn loaded form TableScanResultSet.startKeyGetter.  The startKeyGetter is, I
believe, generated from PredicateList.generateStartKey().  So if you are able to trace through
that method to see which predicate is causing the "null" to be generated, that might be a
good starting point.  Perhaps the short-circuit logic added for DERBY-1357 is somehow leaving
one or more predicates in a state that causes incorrect generation of a null (instead of a
DataValueDescriptor that is "isNull()")?  Again, I'm just guessing--maybe that's helpful,
maybe not...

> 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, query_plan.new, query_plan.old,
test.rar, test.zip, viewer_10_1.zip
>
>
> 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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