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https://issues.apache.org/jira/browse/DERBY-4410?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12767351#action_12767351
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Knut Anders Hatlen commented on DERBY-4410:
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The problem appears to be the logic in
ResultColumnList.expandAllsAndNameColumns(). It goes through the RCL, removes
the asterisks in the list and inserts the columns that the asterisks should
expand to. However, it does not adjust the index variable when it removes and
adds elements in the middle of the very same list that it's iterating over.
When the asterisk expands to more than one column, this makes the loop waste
time on looking for result columns to expand inside the list of already
expanded columns, but it doesn't actually cause any harm. However, if it
expands to an empty column list, the loop will skip the next element in the RCL
because the current list element was removed without decrementing the index
accordingly.
This makes the statement in the bug description fail because t2.* is never
expanded, and it therefore fails with a NullPointerException later when the RCL
is processed by code that expect all such columns to have been expanded.
> NullPointerException when USING clause contains all columns in both join
> tables
> -------------------------------------------------------------------------------
>
> Key: DERBY-4410
> URL: https://issues.apache.org/jira/browse/DERBY-4410
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Affects Versions: 10.6.0.0
> Reporter: Knut Anders Hatlen
> Assignee: Knut Anders Hatlen
>
> ij> create table t(x int);
> 0 rows inserted/updated/deleted
> ij> select t1.*, t2.* from t t1 join t t2 using (x);
> ERROR XJ001: Java exception: ': java.lang.NullPointerException'.
> This statement should have raised an exception because both t1.* and t2.*
> expand to no columns. See DERBY-4407.
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