xiedeyantu opened a new pull request, #21445:
URL: https://github.com/apache/datafusion/pull/21445
## Which issue does this PR close?
- No linked issue.
## Rationale for this change
DataFusion's PostgreSQL unparser should emit PostgreSQL-compatible SQL for
integer casts.`Int8` was still being rendered as `TINYINT`, which is not valid
PostgreSQL syntax. This change makes PostgreSQL output `SMALLINT` instead.
## What changes are included in this PR?
- Added an `int8_cast_dtype` hook to the SQL unparser dialect abstraction.
- Updated `PostgreSqlDialect` to map `Int8` to `SMALLINT`.
- Routed `DataType::Int8` unparsing through the dialect hook.
- Added a regression test covering `select cast(3 as tinyint)]` with
PostgreSQL unparser output.
## Are these changes tested?
- Yes. Ran:
- `cargo test -p datafusion-sql --test sql_integration
cases::plan_to_sql::test_cast_to_tinyint -- --exact`
- The test passes.
## Are there any user-facing changes?
- Yes. PostgreSQL dialect SQL generation now renders `CAST(... AS SMALLINT)`
for `Int8` values instead of `CAST(... AS TINYINT)`.
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