xiedeyantu opened a new pull request, #21226:
URL: https://github.com/apache/datafusion/pull/21226
## Which issue does this PR close?
- Closes #.
## Rationale for this change
DataFusion already supports tuple-like and `STRUCT` comparisons, but the
user-facing documentation did not clearly describe the current comparison
semantics, especially around lexicographical ordering and `NULL` handling. The
`IN` documentation also did not explain tuple-like values.
## What changes are included in this PR?
- Added a short `STRUCT` comparison note to
[struct_coercion.md](/Users/jensen/code/datafusion/docs/source/user-guide/sql/struct_coercion.md),
documenting that:
- `STRUCT` values support standard comparison operators
- comparisons are lexicographical by field order
- `NULL` is ordered before non-`NULL`
- Added minimal examples for `STRUCT` comparisons, including a `NULL` example
- Added a short note to
[subqueries.md](/Users/jensen/code/datafusion/docs/source/user-guide/sql/subqueries.md)
explaining that tuple-like `IN` uses DataFusion's struct equality semantics
- Added a concrete example:
- `SELECT (7521, 30) IN ((7521, NULL));`
- result: `false`
## Are these changes tested?
No new tests were added. This PR only updates documentation for existing
behavior, and the documented behavior is already covered by existing
tuple/struct comparison and `IN` tests.
## Are there any user-facing changes?
Yes. This PR updates the SQL user documentation to clarify the current
semantics of `STRUCT` comparisons and tuple-like `IN` expressions.
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