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From "Mamta A. Satoor (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-3926) Incorrect ORDER BY caused by index
Date Wed, 27 May 2009 16:59:45 GMT

     [ https://issues.apache.org/jira/browse/DERBY-3926?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Mamta A. Satoor updated DERBY-3926:
-----------------------------------

    Attachment: DERBY3926_patch5_052709_stat.txt
                DERBY3926_patch5_052709_diff.txt

I am attaching a new patch, namely DERBY3926_patch5_052709_stat.txt. This patch still does
the same thing as the previous patch which is to make sure that if order by column does not
belong to the outermost optimizable, then check if the order by column has a constant comparison
predicate on it or it is coming from a single-row table. If either of the 2 conditions is
true then we do not need to worry if the outer opitimizable to the optimizable for order by
column are one-row resultsets or not. One thing to note is that I have the additional check
to see if the order by column comes from a single row table. Earlier patch only checked if
the order by column has constant comparison predicate on it. All this logic is now in RequiredRowOrdering:sortRequired(RowOrdering
rowOrdering, JBitSet tableMap, OptimizableList optimizableList) throws StandardException;
This is more logical place for code to be in rather than putting in OptimizerImpl which is
where the previous patch put the code changes.

The one item remaining on this jira is one query from wisconsin that now requires a sorting
node rather than avoiding the sort. Mike and Bryan are right about checking if the previous
optimizables are multi-row optimizables then see if the multiple scan into order by column's
optimizable are all going to return same single row resulset. If so, then there is no need
to require sorting even though outer optimizables are multu-row resultsets.

> Incorrect ORDER BY caused by index
> ----------------------------------
>
>                 Key: DERBY-3926
>                 URL: https://issues.apache.org/jira/browse/DERBY-3926
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.1.3.3, 10.2.3.0, 10.3.3.1, 10.4.2.0
>            Reporter: Tars Joris
>            Assignee: Mamta A. Satoor
>         Attachments: d3926_repro.sql, derby-reproduce.zip, DERBY3926_notforcheckin_patch1_051109_diff.txt,
DERBY3926_notforcheckin_patch1_051109_stat.txt, DERBY3926_notforcheckin_patch2_051109_diff.txt,
DERBY3926_patch3_051509_diff.txt, DERBY3926_patch3_051509_stat.txt, DERBY3926_patch4_051519_diff.txt,
DERBY3926_patch4_051519_stat.txt, DERBY3926_patch5_052709_diff.txt, DERBY3926_patch5_052709_stat.txt,
script3.sql, script3WithUserFriendlyIndexNames.sql, test-script.zip
>
>
> I think I found a bug in Derby that is triggered by an index on a large column: VARCHAR(1024).
I know it  is generally not a good idea to have an index on such a large column.
> I have a table (table2) with a column "value", my query orders on this column but the
result is not sorted. It is sorted if I remove the index on that column.
> The output of the attached script is as follows (results should be ordered on the middle
column):
> ID                  |VALUE        |VALUE
> ----------------------------------------------
> 2147483653          |000002       |21857
> 2147483654          |000003       |21857
> 4294967297          |000001       |21857
> While I would expect:
> ID                  |VALUE        |VALUE
> ----------------------------------------------
> 4294967297          |000001       |21857
> 2147483653          |000002       |21857
> 2147483654          |000003       |21857
> This is the definition:
> CREATE TABLE table1 (id BIGINT NOT NULL, PRIMARY KEY(id));
> CREATE INDEX key1 ON table1(id);
> CREATE TABLE table2 (id BIGINT NOT NULL, name VARCHAR(40) NOT NULL, value VARCHAR(1024),
PRIMARY KEY(id, name));
> CREATE UNIQUE INDEX key2 ON table2(id, name);
> CREATE INDEX key3 ON table2(value);
> This is the query:
> SELECT table1.id, m0.value, m1.value
> FROM table1, table2 m0, table2 m1
> WHERE table1.id=m0.id
> AND m0.name='PageSequenceId'
> AND table1.id=m1.id
> AND m1.name='PostComponentId'
> AND m1.value='21857'
> ORDER BY m0.value;
> The bug can be reproduced by just executing the attached script with the ij-tool.
> Note that the result of the query becomes correct when enough data is changed. This prevented
me from creating a smaller example.
> See the attached file "derby-reproduce.zip" for sysinfo, derby.log and script.sql.
> Michael Segel pointed out:
> "It looks like its hitting the index ordering on id,name from table 2 and is ignoring
the order by clause."

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