cloud-fan opened a new pull request, #49829:
URL: https://github.com/apache/spark/pull/49829
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### What changes were proposed in this pull request?
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This is a long-standing problem. With the GROUP BY ordinal feature, it's
quite easy for users to write a complicated expression as the GROUP BY
expression and also put it in the SELECT list. It's usually OK as the
complicated expressions in the GROUP BY expression and SELECT list remain the
same, but problems may occur with subquery expressions, duplicated relations,
and CTE inline. Let's look at this example:
```
CREATE VIEW v AS
WITH r AS (SELECT c1 + c2 AS c FROM t)
SELECT * FROM r;
SELECT (SELECT max(c) FROM v WHERE c > id) FROM range(1) GROUP BY 1;
```
A scalar subquery appears in both the GROUP BY expression and SELECT list.
The scalar subquery scans table `t`, and because this scalar subquery appears
twice, `DeduplicateRelations` will trigger. This makes the output attributes of
CTE def and ref out of sync in the second scalar subquery and `InlineCTE` will
add a cosmetic `Project` to adjust the output attr ids. `CheckAnalysis` will
inline CTE in the beginning, and this extra cosmetic `Project` in the second
scalar subquery makes Spark think it's not semantically equal to the first
scalar subquery and fails the query.
The proposal here is to remove cosmetic Projects during plan
canonicalization.
### Why are the changes needed?
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bug fix
### Does this PR introduce _any_ user-facing change?
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Yes, some queries fail before and work now.
### How was this patch tested?
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new test
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no
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