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https://issues.apache.org/jira/browse/DERBY-2526?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12487267
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Bryan Pendleton commented on DERBY-2526:
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The query that finds 1 row prints:
Modifying access paths to use join order: 2,1,0, with cost
Level2CostEstimateImpl: at 602878, cost == 216.069408, rowCount ==
0.25920000000000015, singleScanRowCount == 0.6000000000000001
The query that finds 0 rows prints:
Modifying access paths to use join order: 2,0,1, with cost
Level2CostEstimateImpl: at 17715159, cost == 186.67111680000002, rowCount ==
0.1555200000000001, singleScanRowCount == 1.2000000000000002
I believe that optimizable 2 is table b4, optimizable 1 is the UNION view, and
optimizable 0 is table b3, so these results match the other info I was seeing
in the query plan dumps.
Time to fire up the debugger...
> Wrong query results due to column ordering in UNION view
> --------------------------------------------------------
>
> Key: DERBY-2526
> URL: https://issues.apache.org/jira/browse/DERBY-2526
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Affects Versions: 10.0.2.1, 10.1.3.1, 10.2.2.0, 10.3.0.0
> Reporter: Bryan Pendleton
> Attachments: badQuery.log, derby-2526.sql, goodQuery.log
>
>
> I think both select statements in the attached repro script should return 1
> row, but in fact the first statement returns 1 row and the second returns
> zero rows.
> The only difference between the two statements is that the columns in the
> UNION view are listed in a different order (bvw vs. bvw2).
> This seems like a bug to me; the order of the columns in the view definition
> shouldn't matter, should it?
> As Army noted on the derby-dev list, the fact that this reproduces with 10.0
> means that it is not caused by some of the 10.2 optimizer changes. Something
> else is going wrong.
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