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https://issues.apache.org/jira/browse/DERBY-3926?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12702107#action_12702107
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A B commented on DERBY-3926:
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Thanks Mamta!
Could you perhaps include the join order that was chosen for each of the above
queries? I'm not looking for the full query plan, just something short like
the { TENKTUP1, TENKTUP2 } notation. You should be able to get the join order
by reading the query plan top to bottom; the order in which you see the table
names should reflect the join order chosen by the optimizer.
Note that the order by clauses for queries #2 thru #7 all match the "ORDER BY
S.A, T.B" shape that I mentioned in my first April 16th comment, so if the
theory as to how that code is supposed to work was correct, that *might*
explain why these queries fail to avoid the sort when the relevant code is
commented out...? Of course, more tracing/debugging of the individual queries
would be necessary to know for sure...
> 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: 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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