2010YOUY01 commented on code in PR #14271:
URL: https://github.com/apache/datafusion/pull/14271#discussion_r1929505898
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datafusion/expr/src/udaf.rs:
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@@ -635,6 +655,14 @@ pub trait AggregateUDFImpl: Debug + Send + Sync {
fn documentation(&self) -> Option<&Documentation> {
None
}
+
+ /// Indicates whether the aggregation function is monotonic as a set
function. A set
+ /// function is monotonically increasing if its value increases as its
argument grows
+ /// (as a set). Formally, `f` is a monotonically increasing set function
if `f(S) >= f(T)`
+ /// whenever `S` is a superset of `T`.
+ fn monotonicity(&self, _data_type: &DataType) -> AggregateExprMonotonicity
{
Review Comment:
I recommend adding a note at the beginning of the comment: This is used for
a specific (is it BoundedWindowAggExec? )optimization and can be skipped by
using the default implementation.
This interface seems quite difficult to understand for a general user who
only wants to add a simple UDAF
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