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https://issues.apache.org/jira/browse/CALCITE-5756?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17729935#comment-17729935
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Roman Kondakov commented on CALCITE-5756:
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What is the difference with
[ProjectJoinRemoveRule|https://github.com/apache/calcite/blob/main/core/src/main/java/org/apache/calcite/rel/rules/ProjectJoinRemoveRule.java]
> Add Join elimination optimization according to foreign-unique constraint in
> the catalog
> ---------------------------------------------------------------------------------------
>
> Key: CALCITE-5756
> URL: https://issues.apache.org/jira/browse/CALCITE-5756
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: winds
> Priority: Minor
>
> 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.
> 1. Join elimination should be a sub class of TransformationRule and support
> inner join currently.
> 2. Should use
> org.apache.calcite.rel.metadata.RelMetadataQuery#getTableReferences acquire
> Set<RelTableRef>.
> 3. Get constraints by
> org.apache.calcite.plan.RelOptTable#getReferentialConstraints.
> 4. Build the graph by constraints and then remove the redundant join
> according to graph inwardEdges,outwardEdges.
>
> It is very easy to prevent join elimination by not giving the optimizer
> foreign-unique constraint information or don not use the join elimination
> TransformationRule.
>
> 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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