liukun4515 commented on code in PR #1922:
URL: https://github.com/apache/arrow-rs/pull/1922#discussion_r905637663
##########
arrow/src/compute/kernels/cast.rs:
##########
@@ -72,9 +72,9 @@ pub fn can_cast_types(from_type: &DataType, to_type:
&DataType) -> bool {
// cast one decimal type to another decimal type
(Decimal(_, _), Decimal(_, _)) => true,
// signed numeric to decimal
- (Int8 | Int16 | Int32 | Int64 | Float32 | Float64, Decimal(_, _)) |
+ (Null|Int8 | Int16 | Int32 | Int64 | Float32 | Float64, Decimal(_, _))
|
// decimal to signed numeric
- (Decimal(_, _), Int8 | Int16 | Int32 | Int64 | Float32 | Float64)
+ (Decimal(_, _), Null| Int8 | Int16 | Int32 | Int64 | Float32 | Float64)
Review Comment:
> I agree with @nevi-me that a preferable way would be:
>
> 1. Not allow `type` -> `NULL` in the `cast` and `try_cast` kernels
> 2. Add some other function (or maybe just add an example on the `cast`
documentation pointing at `new_null_array` as the way to "cast" any array to
null)
>
> I would personally suggest:
>
> 1. Add support in this PR to cast Decimal --> Null to be consistent with
other `cast` kernels
> 2. As a follow on PR (perhaps to close [Disallow cast from other datatypes
to NullType #1923](https://github.com/apache/arrow-rs/issues/1923)) we can then
remove the `type` -> `NULL` casts
agree with the proposal.
I think this pr can be merged if we follow above suggestion.
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