goldmedal opened a new pull request, #12896:
URL: https://github.com/apache/datafusion/pull/12896
## Which issue does this PR close?
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Closes #.
## Rationale for this change
Consider the following SQL
```SQL
SELECT
c.custkey,
c.name
FROM
(
SELECT
c_custkey as custkey,
c_name as name
FROM
customer
) c
```
The unoptimized plan is
```
Projection: c.custkey, c.name
SubqueryAlias: c
Projection: customer.c_custkey AS custkey, customer.c_name AS name
TableScan: customer
```
However, after the `optimize_projections` rule, the top-level projection
will be removed like
```
SubqueryAlias: c
Projection: customer.c_custkey AS custkey, customer.c_name AS name
TableScan: customer projection=[c_custkey, c_name]
```
The unparsing result would like
```SQL
SELECT
customer.c_custkey AS custkey,
customer.c_name AS "name"
FROM
(
SELECT
customer.c_custkey,
customer.c_name
FROM
customer
) AS c
```
It's an invalid SQL because the column qualifier is the table name
`customer` but it's in the alias `c` scope actually.
<!--
Why are you proposing this change? If this is already explained clearly in
the issue then this section is not needed.
Explaining clearly why changes are proposed helps reviewers understand your
changes and offer better suggestions for fixes.
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## What changes are included in this PR?
When unparsing a `SubqueryAlias` without any projections, we should create
another scope for the alias like
```SQL
SELECT
*
FROM
(
SELECT
customer.c_custkey AS custkey,
customer.c_name AS "name"
FROM
(
SELECT
customer.c_custkey,
customer.c_name
FROM
customer
)
) AS c
```
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sometimes worth providing a summary of the individual changes in this PR.
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## Are these changes tested?
yes
<!--
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1. Prevent the code from being accidentally broken by subsequent changes
2. Serve as another way to document the expected behavior of the code
If tests are not included in your PR, please explain why (for example, are
they covered by existing tests)?
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## Are there any user-facing changes?
The unparsing result is changed.
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updated before approving the PR.
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