Jefffrey commented on code in PR #10304:
URL: https://github.com/apache/arrow-rs/pull/10304#discussion_r3552032653
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arrow-schema/src/datatype.rs:
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@@ -361,12 +361,12 @@ pub enum DataType {
///
/// For example the number 123.45 has precision 5 and scale 2.
///
- /// In certain situations, scale could be negative number. For
- /// negative scale, it is the number of padding 0 to the right
- /// of the digits.
+ /// In certain situations, scale can be negative. Negative scale
+ /// rounds values to the left of the decimal point, and precision is
+ /// the maximum number of non-rounded digits.
///
- /// For example the number 12300 could be treated as a decimal
- /// has precision 3 and scale -2.
+ /// For example, with precision 2 and scale -3, the value 12345 is
+ /// rounded to 12000 and represented as the stored integer 12.
Review Comment:
i find it a little confusing that we talk about how `12345` is converted to
a negative scale decimal here, instead of in cast kernels 🤔
imo at this level all we care about is explaining how values already stored
as decimals are represented and what they actually represent, aka we can say a
value of `12` but with `-3` scale is equivalent to `12000`
(i skimmed the linked discussion so maybe this was already discussed 😅)
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