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From "Jesus Camacho Rodriguez (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HIVE-17040) Join elimination in the presence of FK relationship
Date Wed, 05 Jul 2017 12:51:00 GMT
Jesus Camacho Rodriguez created HIVE-17040:
----------------------------------------------

             Summary: Join elimination in the presence of FK relationship
                 Key: HIVE-17040
                 URL: https://issues.apache.org/jira/browse/HIVE-17040
             Project: Hive
          Issue Type: Sub-task
          Components: Logical Optimizer
    Affects Versions: 3.0.0
            Reporter: Jesus Camacho Rodriguez


If the PK/UK table is not filtered, we can safely remove the join.

A simple example:
{code:sql}
SELECT c_current_cdemo_sk
FROM customer, customer_address
ON c_current_addr_sk = ca_address_sk;
{code}

As a Calcite rule, we could implement this rewriting by 1) matching a Project on top of a
Join operator, 2) checking that only columns from the FK are used in the Project, 3) checking
that the join condition matches the FK - PK/UK relationship, 4) pulling all the predicates
from the PK/UK side and checking that the input is not filtered, and 5) removing the join,
possibly adding a IS NOT NULL condition on the join column from the FK side.

If the PK/UK table is filtered, we should still transform the Join into a SemiJoin operator.



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