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https://issues.apache.org/jira/browse/CALCITE-5756?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17730322#comment-17730322
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Julian Hyde commented on CALCITE-5756:
--------------------------------------
Wow, I was sure we had this already. But we don't. I see that
{{RelOptTable#getReferentialConstraints}} is only used during matching of
materialized views ({{MaterializedViewRule}}, see CALCITE-1731). It would be
great to have this feature.
> Expand ProjectJoinRemoveRule to support inner join remove by the
> 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. Expand ProjectJoinRemoveRule to support inner join remove by the
> foreign-unique constraint in the catalog.
> 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 inner join
> according to graph inwardEdges,outwardEdges.
> 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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