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From "Stan Bradbury (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3926) Incorrect ORDER BY caused by index
Date Sat, 20 Dec 2008 01:04:44 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3926?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12658240#action_12658240
] 

Stan Bradbury commented on DERBY-3926:
--------------------------------------

I verified the report then dropped and recreated the index key3.  The records ordered properly
after that.  Go figure...??  With the newly created cardinality statistics it may be the correct
index is selected this time but the original results are still wrong.

ij> SELECT table1.id, m0.value, m1.value FROM table1, table2 m0, table2 m1 WHERE tab
ER BY m0.value;
ID                  |VALUE
----------------------------------------------------------------------------------
------------------------------------------------------------------------------
2147483653          |000002
2147483654          |000003
4294967297          |000001
3 rows selected

ij> drop index key3;
0 rows inserted/updated/deleted

ij> 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;
ID                  |VALUE
------------------------------------------------------------------------------------
------------------------------------------------------------------------------
4294967297          |000001
2147483653          |000002
2147483654          |000003
3 rows selected

ij> CREATE INDEX key3 ON table2(value);
0 rows inserted/updated/deleted
ij> 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;
ID                  |VALUE
------------------------------------------------------------------------------------
------------------------------------------------------------------------------
4294967297          |000001
2147483653          |000002
2147483654          |000003


3 rows selected

> 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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