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https://issues.apache.org/jira/browse/DERBY-3094?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12572144#action_12572144
]
A B commented on DERBY-3094:
----------------------------
> Here's yet another variant that's hard to explain: the first statement
> works, the second is refused with error 42Y30:
>
> select (a+b)+c, count(*) from t group by c, a+b;
> select a+(b+c), count(*) from t group by c, a+b;
The tree for "(a+b)+c" contains the subtree "a+b" as the left-hand side of the
top-most binary operator and "c" as the right-hand side. Since each of those
matches a stand-alone expression in the GROUP BY, the equivalence checking for
GROUP BY processing passes. But the tree for "a+(b+c)" has "a" on one side and
"b+c" on the other, neither of which shows up as a stand-alone GROUP BY
expression, so the second query is rejected. I agree it's a tad
non-inuititive, but it appears to be "explainable", for what that's worth...
> Here's one other idea that might work:
[ snip ]
> Does this algorithm seem like it would be worth investigating?
Yes, I definitely think this is worth investigating. From what I can tell it
solves the problem of sub-expression substitution, and it seems a tad safer
than pulling unneeded columns into the GROUP BY expression.
There's a CollectNodesVisitor class which finds all instances of a specified
class within the subtree beneath a given ValueNode, so you might be able to use
that to count the number of ColumnReferences in the expression. Though
ColumnReferences tend to appear in lots of places, so it'll be interesting to
see if a simple CollectNodesVisitor is good enough--or will it end up counting
ColumnReferences that shouldn't be counted...?
In any event, +1 to further pursuit of the suggested approach.
> Grouping of expressions causes NullPointerException
> ---------------------------------------------------
>
> Key: DERBY-3094
> URL: https://issues.apache.org/jira/browse/DERBY-3094
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Affects Versions: 10.3.1.4
> Environment: Windows XP, Eclipse 3.2.2, java 1.5.0.11
> Reporter: Peter Balon
> Assignee: Bryan Pendleton
> Priority: Critical
> Attachments: d3094_followup.htm, modifyVisitorDoesntWork.diff,
> notes.html, twoPass.diff, TwoPassForHavingClauseAlso.diff,
> TwoPassVisitor.diff, TwoPassVisitorWithCommentsAndTests.diff
>
>
> Following steps to reproduce the bug:
> create table xx (a double, b double);
> insert into xx values (2, 3);
> select a, a*(b/100.000000), count(*) from xx group by a, a*(b/100.000000);
> Starting run
> select a, a*(b/100.000000), count(*) from xx
> group by a, a*(b/100.000000)
> Run successful
> SQL State = 38000 SQL Code = 20000 SQL Message = Bei der Auswertung eines
> Ausdrucks wurde die Ausnahme 'java.lang.NullPointerException' ausgelöst.
> Exception message = java.sql.SQLException: Bei der Auswertung eines Ausdrucks
> wurde die Ausnahme 'java.lang.NullPointerException' ausgelöst.
> Work around:
> select a, a*(b/100.000000), count(*) from xx group by a, b, a*(b/100.000000)
> Stack trace from application:
> java.sql.SQLException: Bei der Auswertung eines Ausdrucks wurde die Ausnahme
> 'java.lang.NullPointerException' ausgelöst.
> at
> org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(Unknown Source)
> at org.apache.derby.impl.jdbc.Util.newEmbedSQLException(Unknown Source)
> at org.apache.derby.impl.jdbc.Util.seeNextException(Unknown Source)
> at
> org.apache.derby.impl.jdbc.TransactionResourceImpl.wrapInSQLException(Unknown
> Source)
> at
> org.apache.derby.impl.jdbc.TransactionResourceImpl.handleException(Unknown
> Source)
> at org.apache.derby.impl.jdbc.EmbedConnection.handleException(Unknown
> Source)
> at org.apache.derby.impl.jdbc.ConnectionChild.handleException(Unknown
> Source)
> at
> org.apache.derby.impl.jdbc.EmbedResultSet.closeOnTransactionError(Unknown
> Source)
> at org.apache.derby.impl.jdbc.EmbedResultSet.movePosition(Unknown
> Source)
> at org.apache.derby.impl.jdbc.EmbedResultSet.next(Unknown Source)
> at
> de.arcor.billy.report.views.designer.ReportViewerView.setInput(ReportViewerView.java:255)
> at
> de.arcor.billy.report.views.designer.ReportViewerView.createPartControl(ReportViewerView.java:113)
> at
> org.eclipse.ui.internal.ViewReference.createPartHelper(ViewReference.java:332)
> at
> org.eclipse.ui.internal.ViewReference.createPart(ViewReference.java:197)
> at
> org.eclipse.ui.internal.WorkbenchPartReference.getPart(WorkbenchPartReference.java:566)
> at org.eclipse.ui.internal.Perspective.showView(Perspective.java:1675)
> at
> org.eclipse.ui.internal.WorkbenchPage.busyShowView(WorkbenchPage.java:987)
> at
> org.eclipse.ui.internal.WorkbenchPage.access$13(WorkbenchPage.java:968)
> at org.eclipse.ui.internal.WorkbenchPage$13.run(WorkbenchPage.java:3514)
> at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:67)
> at
> org.eclipse.ui.internal.WorkbenchPage.showView(WorkbenchPage.java:3511)
> at
> de.arcor.billy.report.data.ReportDataAdvisor$2.perspectiveChanged(ReportDataAdvisor.java:268)
> at
> de.arcor.billy.system.actions.AbstractOpenPerspectiveActionDelegate$1.run(AbstractOpenPerspectiveActionDelegate.java:66)
> at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:35)
> at
> org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:123)
> at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:3325)
> at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:2971)
> at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:1930)
> at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:1894)
> at
> org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:422)
> at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
> at de.arcor.billy.product.Billy.run(Billy.java:15)
> at
> org.eclipse.core.internal.runtime.PlatformActivator$1.run(PlatformActivator.java:78)
> at
> org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:92)
> at
> org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:68)
> at
> org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:400)
> at
> org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:177)
> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
> at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
> at java.lang.reflect.Method.invoke(Unknown Source)
> at org.eclipse.core.launcher.Main.invokeFramework(Main.java:336)
> at org.eclipse.core.launcher.Main.basicRun(Main.java:280)
> at org.eclipse.core.launcher.Main.run(Main.java:977)
> at org.eclipse.core.launcher.Main.main(Main.java:952)
> Caused by: java.sql.SQLException: Java-Ausnahme: ':
> java.lang.NullPointerException'.
> at
> org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(Unknown Source)
> at org.apache.derby.impl.jdbc.Util.newEmbedSQLException(Unknown Source)
> at org.apache.derby.impl.jdbc.Util.javaException(Unknown Source)
> at
> org.apache.derby.impl.jdbc.TransactionResourceImpl.wrapInSQLException(Unknown
> Source)
> ... 42 more
> Caused by: java.lang.NullPointerException
> at
> org.apache.derby.exe.ac9b638174x0115x5f93x1332x0000046fd8a01b.e10(Unknown
> Source)
> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
> at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
> at java.lang.reflect.Method.invoke(Unknown Source)
> at org.apache.derby.impl.services.reflect.ReflectMethod.invoke(Unknown
> Source)
> at
> org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.doProjection(Unknown
> Source)
> at
> org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.getNextRowCore(Unknown
> Source)
> at
> org.apache.derby.impl.sql.execute.ScrollInsensitiveResultSet.getNextRowFromSource(Unknown
> Source)
> at
> org.apache.derby.impl.sql.execute.ScrollInsensitiveResultSet.getNextRowCore(Unknown
> Source)
> at
> org.apache.derby.impl.sql.execute.BasicNoPutResultSetImpl.getNextRow(Unknown
> Source)
> ... 37 more
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