[jira] Commented: (DERBY-3033) select query results in nullpointer exception in skipScan()

["A B (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DERBY-3033?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12531546 ] 

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

Thank you for the patch, Bryan.  The diff is small and contained and looks functionally correct to me.  I ran the new regression test without your patch and it failed, and with your patch it succeeds.

I do think it might be nice to add explanatory comments to the relevant engine code, so that future readers know *why* it is that we are checking for a "NOT EXISTS" query.  If you'd rather not add comments to the transitive closure code itself, you could perhaps add comments to the FromList.tableNumberIsNotExists() method explaining the scenario in which it is used.  I think there are ample comments in the new ExistsWithSubqueriesTest file, so maybe you could just copy the important bits into the engine code comments, as well?

Aside from that, and assuming derbyall and suites.All ran cleanly, I'm +1 to the commit of this patch.  Many thanks for picking this one up, and for putting so much time into tracking down the cause/solution!

> 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
>            Assignee: Bryan Pendleton
>         Attachments: bug4736.sql, d3033-sane-ij-session-10.3.1.5.txt, generatedActivation.txt, noClosureOfNotExists.diff, patchWithRenamedTest.diff, query_plan.new, query_plan.old, queryPlanRS.txt, repro2.java, repro2.java, repro3.java, 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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