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From "Tars Joris (JIRA)" <j...@apache.org>
Subject [jira] Created: (DERBY-3926) Incorrect ORDER BY caused by index
Date Wed, 29 Oct 2008 08:58:44 GMT
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: 10.4.2.0
            Reporter: Tars Joris
         Attachments: derby-reproduce.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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