dtenedor opened a new pull request, #38052:
URL: https://github.com/apache/spark/pull/38052
### What changes were proposed in this pull request?
There is a bug in the `MergeScalarSubqueries` rule for queries with subquery
expressions nested inside each other, wherein the rule attempts to merge the
nested subquery with its enclosing parent subquery. The result is not a valid
plan and raises an exception in the optimizer. Here is a minimal reproducing
case:
```
sql("create table test(col int) using csv")
checkAnswer(sql("select(select sum((select sum(col) from test)) from
test)"), Row(null))
```
To fix, we disable the optimization for subqueries with nested subqueries
inside them for now.
### Why are the changes needed?
This fixes a bug.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
Updated existing unit tests and added the reproducing case as a new test
case.
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