[jira] [Commented] (CALCITE-5756) Add Join elimination optimization according to foreign-unique constraint in the catalog

["Roman Kondakov (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-5756?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17729935#comment-17729935 ] 

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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