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https://issues.apache.org/jira/browse/DERBY-3880?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12641062#action_12641062
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Kathey Marsden commented on DERBY-3880:
---------------------------------------
Thanks Mamta for looking at this. I think the reason for the difference is that
sourceRow has only 3 columns yet projectMapping has values [3, -1, 5, -1, -1,
2, -1], the third entry (5) does not refer to an actual column so when we get
to
result.setColumn(index + 1, sourceRow.getColumn(projectMapping[index]));
We call ValueRow.getColumn() which is defined as:
public DataValueDescriptor getColumn (int position) {
if (position <= column.length)
return column[position-1];
else
return (DataValueDescriptor)null;
}
and return null because position is greater than column.length.
I found that projectMapping is originally generated in
projectRestrictNode.generateMinion() when we call
int[] mapArray = resultColumns.mapSourceColumns();
ResultColumnList. mapSourceColumns for the column in question executes this
code:
else if (resultColumn.getExpression() instanceof ColumnReference)
{
ColumnReference cr = (ColumnReference)
resultColumn.getExpression();
.....
// Virtual column #s are 1-based
mapArray[index] =
cr.getSource().getVirtualColumnId();
}
Where the resultColumn looks like:
ResultColumn (id=72)
exposedName "##aggregate expression"
virtualColumnId 3
expression ColumnReference (id=74)
columnName "I2"
source ResultColumn (id=76)
exposedName "I2"
virtualColumnId 5
expression VirtualColumnNode (id=94)
sourceColumn ResultColumn (id=100)
exposedName "I2"
virtualColumnId 2
expression VirtualColumnNode
(id=102)
sourceColumn ResultColumn
(id=214)
expression
VirtualColumnNode (id=227)
virtualColumnId 2
sourceColumn
ResultColumn (id=239)
exposedName "I2"
expression BaseColumnNode (id=251)
columnName "I2"
virtualColumnId 2
The virtualColumnId of the ColumnReference under the ##aggregate expression is
*5*, yet there are more deeply nested VirtualColumnNode's with a
virtualColumnId of 2 which I think is correct. I think I need to better
understand mapSourceColumns() and the meaning of this deeply nested
ResultColumn structure to understand what's right here.
Kathey
> NPE on a query with having clause involving a join
> --------------------------------------------------
>
> Key: DERBY-3880
> URL: https://issues.apache.org/jira/browse/DERBY-3880
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Affects Versions: 10.4.2.0
> Environment: Windows 2003 Server
> Reporter: Venkateswaran Iyer
> Priority: Minor
> Attachments: querytree_fail.txt, querytree_works.txt
>
>
> A simple query involving a join and having clause causes a NPE. Any
> subsequent executions cause severe errors. It almost looks like the
> underlying connection was closed out.
> ====
> C:\apps\derby\db-derby-10.4.2.0-bin\db-derby-10.4.2.0-bin\bin>ij
> ij version 10.4
> ij> connect 'jdbc:derby://speed:1527/ClassicModels;user=sa;password=sa
> ';
> ij> create table t1(i int, c varchar(20));
> 0 rows inserted/updated/deleted
> ij> create table t2(i int, c2 varchar(20), i2 int);
> 0 rows inserted/updated/deleted
> ij> insert into t1 values(1, 'abc');
> 1 row inserted/updated/deleted
> ij> insert into t1 values(2, 'abc');
> 1 row inserted/updated/deleted
> ij> insert into t2 values(1, 'xyz', 10);
> 1 row inserted/updated/deleted
> ij> insert into t2 values(1, 'aaa', 20);
> 1 row inserted/updated/deleted
> ij> insert into t2 values(2, 'xxx', 30);
> 1 row inserted/updated/deleted
> ij> select t1.i, avg(t2.i2) from t1 inner join t2 on (t1.i = t2.i) group by
> t1.i
> having avg(t2.i2) > 0;
> ERROR XJ001: DERBY SQL error: SQLCODE: -1, SQLSTATE: XJ001, SQLERRMC:
> java.lang.
> NullPointerException¶¶XJ001.U
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