allisonwang-db opened a new pull request, #38135:
URL: https://github.com/apache/spark/pull/38135
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### What changes were proposed in this pull request?
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This PR supports correlated non-equality predicates in subqueries. It
leverages the DecorrelateInnerQuery framework to decorrelate subqueries with
non-equality predicates. DecorrelateInnerQuery inserts domain joins in the
query plan and the rule RewriteCorrelatedScalarSubquery rewrites the domain
joins into actual joins with the outer query.
Note, correlated non-equality predicates can lead to query plans with
non-equality join conditions, which may be planned as a broadcast NL join or
cartesian product.
### Why are the changes needed?
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To improve subquery support in Spark.
### Does this PR introduce _any_ user-facing change?
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Yes. Before this PR, Spark does not allow correlated non-equality predicates
in subqueries.
For example:
```sql
SELECT (SELECT min(c2) FROM t2 WHERE t1.c1 > t2.c1) FROM t1
```
This will throw an exception: `Correlated column is not allowed in a
non-equality predicate`
After this PR, this query can run successfully.
### How was this patch tested?
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Unit tests and SQL query tests.
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