Jesus Camacho Rodriguez created HIVE-17040:
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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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