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

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

winds created CALCITE-5756:
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             Summary: 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


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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