ozankabak commented on code in PR #13841:
URL: https://github.com/apache/datafusion/pull/13841#discussion_r1892004788


##########
datafusion/expr/src/udf.rs:
##########
@@ -652,8 +659,29 @@ pub trait ScalarUDFImpl: Debug + Send + Sync {
 
     /// Calculates the [`SortProperties`] of this function based on its
     /// children's properties.
-    fn output_ordering(&self, _inputs: &[ExprProperties]) -> 
Result<SortProperties> {
-        Ok(SortProperties::Unordered)
+    fn output_ordering(&self, inputs: &[ExprProperties]) -> 
Result<SortProperties> {
+        if !self.output_preserves_lex_ordering(inputs)? {
+            return Ok(SortProperties::Unordered);
+        }
+
+        let Some(first_order) = inputs.first().map(|p| &p.sort_properties) 
else {
+            return Ok(SortProperties::Unordered);
+        };
+
+        if inputs
+            .iter()
+            .skip(1)
+            .all(|input| &input.sort_properties == first_order)
+        {
+            Ok(*first_order)
+        } else {
+            Ok(SortProperties::Unordered)
+        }
+    }
+
+    /// Whether the function preserves lexicographical ordering based on the 
input ordering
+    fn output_preserves_lex_ordering(&self, _inputs: &[ExprProperties]) -> 
Result<bool> {

Review Comment:
   Seems like you don't need the `output_` prefix, just 
`preserves_lex_ordering` is enough.



##########
datafusion/expr/src/udf.rs:
##########
@@ -809,6 +837,10 @@ impl ScalarUDFImpl for AliasedScalarUDFImpl {
         self.inner.output_ordering(inputs)
     }
 
+    fn output_preserves_lex_ordering(&self, inputs: &[ExprProperties]) -> 
Result<bool> {

Review Comment:
   Seems like you don't need the `output_` prefix, just 
`preserves_lex_ordering` is enough.



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