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https://issues.apache.org/jira/browse/DERBY-3926?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12698038#action_12698038
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Mamta A. Satoor commented on DERBY-3926:
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Yes, even if the cost calculation for a plan is wrong, Derby should not return
wrong resutls and hence for this jira entry, at this point, it might not be
worth it to pursue the lead if the cost calculation is wrong.
I did find one consistently reproducible SQL which will cause the problem
behavior whether we are in the same session where the tables/indexes were
created or whether we start a fresh database session. So, once the database has
been setup, one can open a new ij session and consistently repro the problem
case with following optimizer overrides (this way, one does not have to setup
the whole database in the same session as the origina problem SQL to repro the
problem)
SELECT table1.id, m0.value, m1.value FROM --DERBY-PROPERTIES joinOrder=FIXED
table2 m1 -- DERBY-PROPERTIES index=key3
, table2 m0 -- DERBY-PROPERTIES index=key3
, table1
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;
So, the important thing is have both m1 and m0 use the index KEY3 which is on
the column value on which ordering is happening for table m0.
Now that I have a simple repro case (ie I don't have to go through countless
iteration of optimizer for all different join orders and different predicate
pulling down in different join orders), I can focus on the problem join order.
> 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
> 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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