viirya commented on code in PR #1922:
URL: https://github.com/apache/arrow-rs/pull/1922#discussion_r904163992
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arrow/src/compute/kernels/cast.rs:
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@@ -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:
Hmm, is it allowable to cast Decimal type to Null type? It looks a bit weird
to me. For example, I re-checked Spark and it doesn't allow this kind of
casting (anytype to NullType).
I also checked C++ Cast kernels. Mostly the datatypes cannot cast to
NullType (e.g.
https://github.com/apache/arrow/blob/53752adc6b81166cd4ee7db5a819494042f29197/cpp/src/arrow/compute/kernels/scalar_cast_test.cc#L187-L211).
I said "mostly" because I don't see explicit tests for other cases like
Decimal, but I suspect that it is not allowed but just lack of test coverage.
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