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https://issues.apache.org/jira/browse/CALCITE-5756?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17736932#comment-17736932
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Julian Hyde commented on CALCITE-5756:
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ForeignKeys returning an ImmutableBitSet doesn’t seem to have enough
information. First, it doesn’t say what table each column references. Second,
it doesn’t allow composite foreign keys.
To eliminate the join to DEPT, it’s not sufficient that you know EMP.DEPTNO is
a foreign key. You have to know that it is a foreign key to the DEPT table. Do
you check that in the code?
> Expand ProjectJoinRemoveRule to support inner join removal by using the
> foreign-unique constraints
> --------------------------------------------------------------------------------------------------
>
> Key: CALCITE-5756
> URL: https://issues.apache.org/jira/browse/CALCITE-5756
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: winds
> Assignee: winds
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.35.0
>
>
> Join elimination is a useful optmize improvement.
> Consider a query that joins the two tables but does not make use of the Dept
> columns:
> {code:java}
> SELECT Emp.name, Emp.salary
> FROM Emp, Dept
> WHERE Emp.deptno = Dept.dno {code}
> Assuming Emp.deptno is the foreign-key and is non-null, Dept.dno is the
> unique-key. The sql above can be rewritten as following. remove the Dept
> table without affecting the resultset.
> {code:java}
> SELECT Emp.name, Emp.salary
> FROM Emp {code}
> Without redundant join elimination, this query execution may perform poorly.
> The optimize improvement is also available in SQL Server, Oracle and
> Snowflake and so on.
> In Calcite, i think that is also useful. The infrastructure that join
> elimination depend on is already available.
> The main steps are as follows:
> 1. Analyse the column used by project, and then split them to left and right
> side.
> 2. Acccording to the project info above and outer join type, bail out in some
> scene.
> 3. Get join info such as join keys.
> 4. For inner join check foreign and unique keys, these may use
> RelMetadataQuery#getForeignKeys(newly add, similar to
> RelMetadataQuery#getUniqueKeys),
> RelOptTable#getReferentialConstraints.
> 5. Check removing side join keys are areColumnsUnique both for outer join and
> inner join.
> 6. If all done, calculate the fianl project and transform.
> Please help me to check the improvement whether is useful or not.
> And i would like to add this improvement to Calcite.
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