alamb commented on code in PR #11989:
URL: https://github.com/apache/datafusion/pull/11989#discussion_r1723667256
##########
datafusion/expr/src/udaf.rs:
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@@ -552,6 +570,14 @@ pub trait AggregateUDFImpl: Debug + Send + Sync {
fn is_descending(&self) -> Option<bool> {
None
}
+
+ /// Returns default value of the function given the input is all `null`.
+ ///
+ /// Most of the aggregate function return Null if input is Null,
+ /// while `count` returns 0 if input is Null
+ fn default_value(&self, data_type: &DataType) -> Result<ScalarValue> {
+ ScalarValue::try_from(data_type)
+ }
}
Review Comment:
Maybe we can improve the docuemention?
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