xudong963 commented on code in PR #15503:
URL: https://github.com/apache/datafusion/pull/15503#discussion_r2030735470


##########
datafusion/physical-plan/src/execution_plan.rs:
##########
@@ -427,6 +427,16 @@ pub trait ExecutionPlan: Debug + DisplayAs + Send + Sync {
         Ok(Statistics::new_unknown(&self.schema()))
     }
 
+    /// Returns statistics for each partition of this `ExecutionPlan` node.
+    /// If statistics are not available, returns an array of
+    /// [`Statistics::new_unknown`] for each partition.
+    fn statistics_by_partition(&self) -> Result<Vec<Statistics>> {
+        Ok(vec![
+            Statistics::new_unknown(&self.schema());
+            self.properties().partitioning.partition_count()
+        ])

Review Comment:
   I noticed the original default implementation from you; it's a bit risky if 
a node doesn't have a specific implementation for the API, and I also think 
most of the nodes' partition statistics don't follow the "repeating the global 
statistics for each partition". So out of safety, I change it to `unknown 
statistics`.



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