kasakrisz commented on code in PR #6360:
URL: https://github.com/apache/hive/pull/6360#discussion_r2959922437
##########
ql/src/test/queries/clientpositive/empty_result_correlate2.q:
##########
@@ -0,0 +1,22 @@
+set hive.support.concurrency=true;
+set hive.txn.manager=org.apache.hadoop.hive.ql.lockmgr.DbTxnManager;
+
+-- To create a HiveValues operator before decorrelation automatic query
rewrite with
+-- materialized views is used.
+-- All tables must be transactional to trigger automatic query rewrite.
+create table mv_source (any_col int) stored as orc TBLPROPERTIES
('transactional'='true');
+create table t1 (a int, b int) stored as orc TBLPROPERTIES
('transactional'='true');
+create table t2 (a int, b int) stored as orc TBLPROPERTIES
('transactional'='true');
+
+-- At least one materialized view must exist.
+create materialized view any_mv as
+select any_col from mv_source where any_col > 20;
+
+-- Automatic query rewrite traverses the plan and recreates the HiveFilter
using RelBuilder.
+-- If the condition is always false, it replaces the filter with HiveValues.
+explain cbo
+select * from t1 where 1 = 2
+union
+select * from t1
+where exists (select a from t2 where t1.a > 10)
Review Comment:
The rules
* HiveRemoveEmptySingleRules.CORRELATE_LEFT_INSTANCE
* HiveRemoveEmptySingleRules.CORRELATE_RIGHT_INSTANCE
expect that the empty `Values` is one of the inputs of the `Correlate`.
However, if the plan contains an operator with multiple inputs (ex. Union)
and one of the input is an empty branch, decorrelation is aborted—even when the
`Correlate` is in a different input. Please see the unit test I added to the PR
for an example.
https://github.com/apache/hive/blob/d55885ee5ef5036c3371ccd46cd46fa20715a58e/ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveRelDecorrelator.java#L389-L394
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