xudong963 commented on code in PR #15852:
URL: https://github.com/apache/datafusion/pull/15852#discussion_r2065927159


##########
datafusion/physical-plan/src/aggregates/mod.rs:
##########
@@ -941,49 +994,15 @@ impl ExecutionPlan for AggregateExec {
     }
 
     fn statistics(&self) -> Result<Statistics> {
-        // TODO stats: group expressions:
-        // - once expressions will be able to compute their own stats, use it 
here
-        // - case where we group by on a column for which with have the 
`distinct` stat
-        // TODO stats: aggr expression:
-        // - aggregations sometimes also preserve invariants such as min, 
max...
-        let column_statistics = Statistics::unknown_column(&self.schema());
-        match self.mode {
-            AggregateMode::Final | AggregateMode::FinalPartitioned
-                if self.group_by.expr.is_empty() =>
-            {
-                Ok(Statistics {
-                    num_rows: Precision::Exact(1),
-                    column_statistics,
-                    total_byte_size: Precision::Absent,
-                })
-            }
-            _ => {
-                // When the input row count is 0 or 1, we can adopt that 
statistic keeping its reliability.
-                // When it is larger than 1, we degrade the precision since it 
may decrease after aggregation.
-                let num_rows = if let Some(value) =
-                    self.input().statistics()?.num_rows.get_value()
-                {
-                    if *value > 1 {
-                        self.input().statistics()?.num_rows.to_inexact()
-                    } else if *value == 0 {
-                        // Aggregation on an empty table creates a null row.
-                        self.input()
-                            .statistics()?
-                            .num_rows
-                            .add(&Precision::Exact(1))
-                    } else {
-                        // num_rows = 1 case
-                        self.input().statistics()?.num_rows
-                    }
-                } else {
-                    Precision::Absent
-                };
-                Ok(Statistics {
-                    num_rows,
-                    column_statistics,
-                    total_byte_size: Precision::Absent,
-                })
-            }
+        self.statistics()

Review Comment:
   I changed to `statistics_inner`, it's good to avoid confusion, thanks!



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