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From "Dag H. Wanvik (JIRA)" <j...@apache.org>
Subject [jira] Issue Comment Edited: (DERBY-4450) GROUP BY in an IN-subquery inside HAVING clause whose select list is subset of group by columns, gives NPE
Date Thu, 19 Nov 2009 00:23:39 GMT

    [ https://issues.apache.org/jira/browse/DERBY-4450?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12779755#action_12779755
] 

Dag H. Wanvik edited comment on DERBY-4450 at 11/19/09 12:23 AM:
-----------------------------------------------------------------

The problem here is that an extra PRN is added for this case in
SelectNode to project away the unselected group by columns. This PRN
is added at the end of SelectNode#genProjectRestrict, ca line 1620.

However, the predicate of the PRN (for the "IN") constructed in
SubqueryNode#pushNewPredicate as a part of SubqueryNode#preprocess,
has already happened, and knows nothing of the new PRN added by
SelectNode for this case.

The consequence is that the IN predicate at code generation time has a
result column list corresponding to the inner Select node (later
becoming a PRN), not the PRN sitting on top of it and thus has a wrong
idea of what result set number to use at execution time. In this case,
the subquery's rows are materialized and the SelectNode/PRN result set
is closed after this is done. Closing clears the current row for that
result set.

But since the generated code "thinks" that the result set number for
the SelectNode/PRN is sitting directly below it, it uses that result
set number when it synthesizes the materialized UnionResultSet, it
*reuses* that result set number for the UnionResultSet,
cf. BaseActivation#materializeResultSetIfPossible.

In reality, at run-time, that result set is two levels below the
Subquery (AnyResultSet in this case). So, when the predicate is
evaluated it gives the NPE, since it accesses a result set two levels
below it, which has already been closed by the materialization, and
would have been wrong anyway, since the projection PRN is necessary
and the IN's PRN predicate needs to have the correct view of what's under it.

A possible solution would be to reuse the result column list from the
original Select in the PRN added by for group by's projection, so the
the IN predicate would point to the right result set at code
generation time. I think that trick is used elsewhere.


      was (Author: dagw):
    The problem here is that an extra PRN is added for this case in
SelectNode to project away the unselected group by columns. This PRN
is added at the end of SelectNode#genProjectRestrict, ca line 1620.

However, the predicate of the PRN (for the "IN") constructed in
SubqueryNode#pushNewPredicate as a part of SubqueryNode#preprocess,
has already happened, and knows nothing of the new PRN added by
SelectNode for this case.

The consequence is that the IN predicate at code generation time has a
result column list corresponding to the inner Select node (later
becoming a PRN), not the PRN sitting on top of it and thus has a wrong
idea of what result set number to use at execution time. In this case,
the subquery's rows are materialized and the SelectNode/PRN result set
is closed after this is done. Closing clears the current row for that
result set.

But since the generated code "thinks" that the result set number for
the SelectNode/PRN is sitting directly below it, it uses that result
set number when it synthesizes the materialized UnionResultSet, it
*reuses* that result set number for the UnionResultSet,
cf. BaseActivation#materializeResultSetIfPossible.

In reality, at run-time, that result set is two levels below the
Subquery (AnyResultSet in this case). So, when the predicate is
evaluated it gives the NPE, since it accesses a result set two levels
below it, which has already been closed by the materialization, and
would have been wrong anyway, since the projection PRN is necessary
and the predicate needs to have the correct view of what's under it.

A possible solution would be to reuse the result column list from the
original Select in the PRN added by for group by's projection, so the
the IN predicate would point to the right result set at code
generation time. I think that trick is used elsewhere.

  
> GROUP BY in an IN-subquery inside HAVING clause whose select list is subset of group
by columns, gives NPE
> ----------------------------------------------------------------------------------------------------------
>
>                 Key: DERBY-4450
>                 URL: https://issues.apache.org/jira/browse/DERBY-4450
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>            Reporter: Dag H. Wanvik
>
> Found this while working on DERBY-4397 for a similar case with ORDER BY inside an IN-subquery:
> Repro:
> create table t(i int not null, constraint c unique (i), j int, k int);
> insert into t values (1,10,1),(2,40,1),(3,45,1),(4,46,1),(5,90,1);
> select sum(j) from t group by i having i in (select i from t group by i,j );
> gives NPE:
> ERROR XJ001: Java exception: ': java.lang.NullPointerException'.
> java.sql.SQLException: Java exception: ': java.lang.NullPointerException'.
> 	at org.apache.derby.impl.jdbc.SQLExceptionFactory40.getSQLException(SQLExceptionFactory40.java:95)
> 	at org.apache.derby.impl.jdbc.Util.newEmbedSQLException(Util.java:87)
> 	at org.apache.derby.impl.jdbc.Util.javaException(Util.java:244)
> 	at org.apache.derby.impl.jdbc.TransactionResourceImpl.wrapInSQLException(TransactionResourceImpl.java:403)
> 	at org.apache.derby.impl.jdbc.TransactionResourceImpl.wrapInSQLException(TransactionResourceImpl.java:398)
> 	at org.apache.derby.impl.jdbc.TransactionResourceImpl.handleException(TransactionResourceImpl.java:346)
> 	at org.apache.derby.impl.jdbc.EmbedConnection.handleException(EmbedConnection.java:2201)
> 	at org.apache.derby.impl.jdbc.ConnectionChild.handleException(ConnectionChild.java:81)
> 	at org.apache.derby.impl.jdbc.EmbedResultSet.closeOnTransactionError(EmbedResultSet.java:4338)
> 	at org.apache.derby.impl.jdbc.EmbedResultSet.movePosition(EmbedResultSet.java:467)
> 	at org.apache.derby.impl.jdbc.EmbedResultSet.next(EmbedResultSet.java:371)
> 	at org.apache.derby.tools.JDBCDisplayUtil.indent_DisplayResults(JDBCDisplayUtil.java:382)
> 	at org.apache.derby.tools.JDBCDisplayUtil.indent_DisplayResults(JDBCDisplayUtil.java:338)
> 	at org.apache.derby.tools.JDBCDisplayUtil.indent_DisplayResults(JDBCDisplayUtil.java:241)
> 	at org.apache.derby.tools.JDBCDisplayUtil.DisplayResults(JDBCDisplayUtil.java:229)
> 	at org.apache.derby.impl.tools.ij.utilMain.displayResult(utilMain.java:448)
> 	at org.apache.derby.impl.tools.ij.utilMain.doCatch(utilMain.java:522)
> 	at org.apache.derby.impl.tools.ij.utilMain.runScriptGuts(utilMain.java:363)
> 	at org.apache.derby.impl.tools.ij.utilMain.go(utilMain.java:261)
> 	at org.apache.derby.impl.tools.ij.Main.go(Main.java:229)
> 	at org.apache.derby.impl.tools.ij.Main.mainCore(Main.java:184)
> 	at org.apache.derby.impl.tools.ij.Main.main(Main.java:75)
> 	at org.apache.derby.tools.ij.main(ij.java:59)
> Caused by: java.sql.SQLException: Java exception: ': java.lang.NullPointerException'.
> 	at org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(SQLExceptionFactory.java:45)
> 	at org.apache.derby.impl.jdbc.SQLExceptionFactory40.wrapArgsForTransportAcrossDRDA(SQLExceptionFactory40.java:119)
> 	at org.apache.derby.impl.jdbc.SQLExceptionFactory40.getSQLException(SQLExceptionFactory40.java:70)
> 	... 22 more
> Caused by: java.lang.NullPointerException
> 	at org.apache.derby.impl.sql.execute.BaseActivation.getColumnFromRow(BaseActivation.java:1451)
> 	at org.apache.derby.exe.acf81e0010x0125x09b5xf628x000003d4bf801.e5(Unknown Source)
> 	at org.apache.derby.impl.services.reflect.DirectCall.invoke(ReflectGeneratedClass.java:149)
> 	at org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.getNextRowCore(ProjectRestrictResultSet.java:268)
> 	at org.apache.derby.impl.sql.execute.AnyResultSet.getNextRowCore(AnyResultSet.java:171)
> 	at org.apache.derby.exe.acf81e0010x0125x09b5xf628x000003d4bf801.g0(Unknown Source)
> 	at org.apache.derby.exe.acf81e0010x0125x09b5xf628x000003d4bf801.e3(Unknown Source)
> 	at org.apache.derby.impl.services.reflect.DirectCall.invoke(ReflectGeneratedClass.java:145)
> 	at org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.getNextRowCore(ProjectRestrictResultSet.java:268)
> 	at org.apache.derby.impl.sql.execute.BasicNoPutResultSetImpl.getNextRow(BasicNoPutResultSetImpl.java:471)
> 	at org.apache.derby.impl.jdbc.EmbedResultSet.movePosition(EmbedResultSet.java:427)

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