filipdavidovic opened a new pull request, #54137:
URL: https://github.com/apache/spark/pull/54137
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### What changes were proposed in this pull request?
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Add support for alias in PIVOT clause, following the same syntax as
[T-SQL](https://learn.microsoft.com/en-us/sql/t-sql/queries/from-using-pivot-and-unpivot?view=sql-server-ver17)
and
[BigQuery](https://docs.cloud.google.com/bigquery/docs/reference/standard-sql/query-syntax#pivot_operator).
Short spec to describe the improvement:
> Extend the `PIVOT` clause to accept an optional alias (`PIVOT (...) AS
alias`), allowing the pivoted result set to be referenced by name in the
surrounding query context. The alias qualifies all columns produced by the
pivot operation, including both the grouping columns and the dynamically
generated value columns. When an alias is provided, columns may be referenced
as `alias.column_name`. When omitted, current unqualified resolution behaviour
is preserved. In queries with multiple pivots or joins, the alias disambiguates
column references. The alias scope is limited to the query block in which the
pivot appears.
### Why are the changes needed?
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Main reason for the improvement is parity with platforms like SQL Server and
Snowflake. When customers want to migrate, their queries using PIVOT alias
can't be automatically transpiled, requiring a human in the loop.
### Does this PR introduce _any_ user-facing change?
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Yes, it introduces an optional alias and updates the documentation to
reflect it. Change is fully backwards compatible.
### How was this patch tested?
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Added end-to-end tests in `SQLQueryTestSuite` and unit tests in
`PivotParserSuite`.
```bash
build/sbt "catalyst/testOnly *PivotParserSuite"
build/sbt "sql/testOnly *SQLQueryTestSuite -- -z pivot.sql"
```
### Was this patch authored or co-authored using generative AI tooling?
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Implemented with help of Claude Code.
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