Stamatis Zampetakis created HIVE-27296:
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Summary: HiveRelDecorrelator does not handle correlation with
Values
Key: HIVE-27296
URL: https://issues.apache.org/jira/browse/HIVE-27296
Project: Hive
Issue Type: Bug
Reporter: Stamatis Zampetakis
Assignee: Stamatis Zampetakis
The {{HiveRelDecorrelator}} does not cope well with {{Values}} expressions and
when such expression exists in the plan it fails to remove the respective
{{Correlate}}.
In HIVE-27298, we discovered a query that has a correlation over an empty
{{Values}} expression.
{code:sql}
EXPLAIN CBO SELECT id FROM t1 WHERE NULL IN (SELECT NULL FROM t2 where t1.id =
t2.id);{code}
The CBO plan after decorrelation is shown below.
{noformat}
HiveProject(id=[$0])
LogicalCorrelate(correlation=[$cor0], joinType=[semi], requiredColumns=[{}])
HiveTableScan(table=[[default, t1]], table:alias=[t1])
HiveValues(tuples=[[]])
{noformat}
Although, in HIVE-27298 we could find a solution for a plan that contains an
empty {{Values}} there can be queries with correlations on non-empty {{Values}}
and for those we don't have a solution at the moment.
Normally after decorrelation we shouldn't have any {{Correlate}} expressions in
the plan.
The problem starts from
[HiveRelDecorrelator.decorrelate(Values)|https://github.com/apache/hive/blob/59058c65457fb7ab9d8575a555034e6633962661/ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveRelDecorrelator.java#L471]
that returns null when it encounters the {{Values}} expression.
Later, in
[HiveRelDecorrelator.decorrelate(Correlate)|https://github.com/apache/hive/blob/59058c65457fb7ab9d8575a555034e6633962661/ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveRelDecorrelator.java#L1247]
it will bail out when treating the {{Correlate}} since one of the inputs is
not rewritten.
The problem is still there in latest Calcite (CALCITE-5568).
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