sunchao opened a new pull request, #1607:
URL: https://github.com/apache/arrow-rs/pull/1607
# Which issue does this PR close?
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Closes #1606.
# Rationale for this change
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For decimal type, it is a valid case for scale to be equal to precision.
However currently the `PrimitiveTypeBuilder` will return error in such case.
```rust
if self.scale >= self.precision {
return Err(general_err!(
"Invalid DECIMAL: scale ({}) cannot be greater than or equal to
precision \
({})",
self.scale,
self.precision
));
```
It seems the Parquet [logical type specification for decimal
type](https://github.com/apache/parquet-format/blob/master/LogicalTypes.md#decimal)
is also incorrect on this:
> If not specified, the scale is 0. Scale must be zero or a positive integer
**less than** the precision. Precision is required and must be a non-zero
positive integer. A precision too large for the underlying type (see below) is
an error.
Both
[Java](https://github.com/apache/parquet-mr/blob/master/parquet-column/src/main/java/org/apache/parquet/schema/Types.java#L618)
and
[C++](https://github.com/apache/arrow/blob/master/cpp/src/parquet/types.cc#L976)
implementation allows scale to be equal to precision.
# What changes are included in this PR?
Fix the schema validation and allow the case when scale is equal to
precision. Added a test for this.
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# Are there any user-facing changes?
- Yes, the behavior is fixed after the PR, where users can now construct
decimal logical type where scale is equal to precision, such as `Decimal(5, 5)`.
- There is no API change introduced.
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