milenkovicm commented on code in PR #9906:
URL: https://github.com/apache/datafusion/pull/9906#discussion_r1587483960
##########
datafusion/expr/src/udwf.rs:
##########
@@ -266,6 +290,35 @@ pub trait WindowUDFImpl: Debug + Send + Sync {
fn aliases(&self) -> &[String] {
&[]
}
+
+ /// Optionally apply per-UDWF simplification / rewrite rules.
+ ///
+ /// This can be used to apply function specific simplification rules during
+ /// optimization. The default implementation does nothing.
+ ///
+ /// Note that DataFusion handles simplifying arguments and "constant
+ /// folding" (replacing a function call with constant arguments such as
+ /// `my_add(1,2) --> 3` ). Thus, there is no need to implement such
+ /// optimizations manually for specific UDFs.
+ ///
+ /// Example:
+ /// [`advanced_udwf.rs`]:
<https://github.com/apache/arrow-datafusion/blob/main/datafusion-examples/examples/advanced_udwf.rs>
+ ///
+ /// # Returns
+ /// [`ExprSimplifyResult`] indicating the result of the simplification NOTE
+ /// if the function cannot be simplified, the arguments *MUST* be returned
+ /// unmodified
+ fn simplify(
+ &self,
+ args: Vec<Expr>,
+ _partition_by: &[Expr],
Review Comment:
It would be great if we would not need do to decompose and then compose
function again, something like:
```rust
Expr::AggregateFunction(AggregateFunction {
func_def:AggregateFunctionDefinition::UDF(ref udaf),
ref args,
ref distinct,
ref filter,
ref order_by,
ref null_treatment }) => {
match udaf.simplify(args, distinct, &filter, &order_by,
&null_treatment)? {
ExprSimplifyResult::Simplified(simplified) =>
Transformed::yes(simplified),
ExprSimplifyResult::Original(_) => Transformed::no(expr),
}
}
```
clone of args could be avoided if simplify returns empty vector ... but that
breaks semantics of the api
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