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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