viirya commented on code in PR #2357:
URL: https://github.com/apache/arrow-rs/pull/2357#discussion_r940614439
##########
arrow/src/compute/kernels/cast.rs:
##########
@@ -1276,8 +1277,17 @@ fn cast_decimal_to_decimal(
.iter()
.map(|v| v.map(|v| v.as_i128() * mul))
.collect::<Decimal128Array>()
- }
- .with_precision_and_scale(*output_precision, *output_scale)?;
+ };
+ // For decimal cast to decimal, if the range of output is gt_eq than the
input, don't need to
+ // do validation.
+ let output_array = match output_precision-output_scale>=input_precision -
input_scale {
+ true => {
+ output_array.with_precision_and_scale(*output_precision,
*output_scale, false)
+ }
+ false => {
+ output_array.with_precision_and_scale(*output_precision,
*output_scale, true)
+ }
+ }?;
Review Comment:
> if cast decimal(5,2) to decimal(5,3). a value of 123.45 will be convert to
123.450, but the 123450 is out of range of decimal(5,3).
This out-of-range should already be caught now as `with_precision_and_scale`
will do the validation.
But I got your point of the change here. `with_precision_and_scale` will do
validation here all the time. But for some cases `output precision >= input
precision + (output scale - input scale)`, we can skip the validation.
I'd suggest to rewrite the condition as `output precision >= input precision
+ (output scale - input scale)`.
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