fatmanverse opened a new pull request, #12920:
URL: https://github.com/apache/seatunnel/pull/12920
Fixes #12915
### Purpose of this pull request
`SystemFunction#castAs` rounded `CAST(x AS DECIMAL(p,s))` with
`RoundingMode.CEILING` for DECIMAL and STRING sources, and with `HALF_UP` for
FLOAT and DOUBLE (#11523). (Integral sources took the CEILING branch too, but
never drop digits.) The same value gave a different DECIMAL depending on its
source type, and the CEILING results differ from `CAST` in MySQL, PostgreSQL
and H2: `CAST(1.21 AS DECIMAL(6,1))` gave `1.3` and `CAST(-1.25 AS
DECIMAL(6,1))` gave `-1.2`.
All source types now round half away from zero. Float/Double are still
converted from their exact binary value first, as #11523 introduced.
Impact checked:
- Only the DECIMAL branch of `castAs` changes. `CEIL`/`CEILING`, `FLOOR`,
`ROUND` and `TRUNC` in `NumericFunction` keep their own rounding modes.
- Casts that do not drop digits are unchanged. The e2e configs that cast to
DECIMAL (`func_system.conf`: `"12.4"` -> `12.40`, a BIGINT ->
`1687747869032.0000`; `jdbc_to_jdbc_with_transform.conf`) do not drop digits.
- `SystemFunctionTest#testCastAsDecimalRounding` pinned the CEILING result
(`"1.234"` -> `1.24`); it now expects `1.23`.
### Does this PR introduce _any_ user-facing change?
Yes. Casting a DECIMAL or STRING value to a smaller scale can return a
different last digit. This is documented in `incompatible-changes.md` (en/zh),
and the CAST section of `sql-functions.md` (en/zh) now states the rounding rule.
### How was this patch tested?
- `SystemFunctionTest`: DECIMAL, STRING and DOUBLE sources give the same
result for positive, negative, tie and below-half values, integral sources are
unchanged, and the same check runs through the SQL transform.
`seatunnel-transforms-v2` unit tests pass on JDK 17, except
`LLMBooleanOutputTest#readsLegacyFactoryWrapperWithValidationDisabled`, which
fails the same way on dev (`InvalidClassException` on
`AbstractMultiCatalogTransform`).
- On a Zeta cluster, FakeSource -> Sql -> Jdbc (MySQL) with `1.21`, `-1.21`,
`-1.25` as DECIMAL, STRING and DOUBLE: before `1.3/1.3/1.2`, `-1.2/-1.2/-1.2`,
`-1.2/-1.2/-1.3`; now `1.2`, `-1.2`, `-1.3` for all three, the same as MySQL
`CAST`.
### Check list
* [ ] If any new Jar binary package adding in your PR, please add License
Notice according
[New License
Guide](https://github.com/apache/seatunnel/blob/dev/docs/en/developer/new-license.md)
* [x] If necessary, please update the documentation to describe the new
feature. https://github.com/apache/seatunnel/tree/dev/docs
* [x] If necessary, please update `incompatible-changes.md` to describe the
incompatibility caused by this PR.
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