liukun4515 commented on a change in pull request #1408:
URL: https://github.com/apache/arrow-datafusion/pull/1408#discussion_r771180890



##########
File path: datafusion/src/physical_plan/expressions/average.rs
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@@ -102,7 +114,14 @@ impl AggregateExpr for Avg {
     }
 
     fn field(&self) -> Result<Field> {
-        Ok(Field::new(&self.name, DataType::Float64, true))
+        Ok(Field::new(&self.name, self.data_type.clone(), true))
+    }
+
+    fn create_accumulator(&self) -> Result<Box<dyn Accumulator>> {
+        Ok(Box::new(AvgAccumulator::try_new(
+            // avg is f64 or decimal
+            &self.data_type,

Review comment:
       The result type of phy expr(sum/avg) is same with each Accumulator, and 
it was decided by `sum_return_type` and `avg_return_type`.
   
   If the column is decimal(8,2), the avg of this column must be less than 
`10^10-1`, but we need more digits to represent the decimal part. For example, 
The avg of `3,4,6` is `4.333333.....`, we should increase the scale part.
   




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