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https://issues.apache.org/jira/browse/ARROW-18334?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17634553#comment-17634553
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Weston Pace commented on ARROW-18334:
-------------------------------------
Example output type resolver (from [~bkietz]):
{noformat}
Result<TypeHolder> FirstTimestampType(KernelContext*, const
std::vector<TypeHolder>& types) {
for (const auto& type : types) {
if (type.id() == Type::TIMESTAMP) return type;
}
return Status::Invalid("no timestamp type found");
}
{noformat}
> add function for timestamp/duration is not commutative
> ------------------------------------------------------
>
> Key: ARROW-18334
> URL: https://issues.apache.org/jira/browse/ARROW-18334
> Project: Apache Arrow
> Issue Type: Bug
> Components: C++
> Reporter: Weston Pace
> Priority: Major
>
> The expression simplification currently has a small set of functions which it
> knows are commutative (IsBinaryAssociativeCommutative). "add" (and
> "add_checked" are in this list. This should be ok for
> add(timestamp,duration) since this boils down to add(int64,int64) which is
> commutative. However, the way the kernels are currently implemented, we are
> getting the incorrect output type.
> Concretely, we have kernels:
> {noformat}
> add_checked<Timestamp,Duration>() -> types[0]
> add_checked<Duration,Timestamp>() -> types[1]
> {noformat}
> A call is made with expression {{field_ref("x") + duration_literal}}. This
> call is bound to {{add_checked<Timestamp, Duration>}}. However, the
> expression is then simplified to {{duration_literal + field_ref("x")}}.
> Oddly enough, the math in this case is correct, since it is just addition,
> but the output type is not. It assigns an output type of duration instead of
> timestamp.
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