jayzhan211 commented on code in PR #10268:
URL: https://github.com/apache/datafusion/pull/10268#discussion_r1586955192
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datafusion/expr/src/signature.rs:
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@@ -92,14 +92,22 @@ pub enum TypeSignature {
/// A function such as `concat` is `Variadic(vec![DataType::Utf8,
DataType::LargeUtf8])`
Variadic(Vec<DataType>),
/// One or more arguments of an arbitrary but equal type.
- /// DataFusion attempts to coerce all argument types to match the first
argument's type
+ /// DataFusion attempts to coerce all argument types to match to the
common type with comparision coercion.
///
/// # Examples
/// Given types in signature should be coercible to the same final type.
/// A function such as `make_array` is `VariadicEqual`.
///
/// `make_array(i32, i64) -> make_array(i64, i64)`
VariadicEqual,
+ /// One or more arguments of an arbitrary but equal type or Null.
+ /// Non-comparison coercion is attempted to match the signatures.
+ ///
+ /// Functions like `coalesce` is `VariadicEqual`.
Review Comment:
yes. `Non-comparison coercion` is `type_union_resolution`
Actually, I think `type_union_resolution` is what we really need for
coercion. Current `comparison_coercion` may not exist in the long term because
I think there are many `workaround` solutions included in it, and those are
possible to pull out to their **correct places**.
Ideally, we could shape `comparison_coercion` to more like
`type_union_resolution`. But, adjusting logic inside it is error-prone if the
test is not covered.
At least I can tell the dict-coercion is different between these two now.
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