pengbo opened a new pull request #24286: [SPARK-27351][SQL] Wrong outputRows 
estimation after AggregateEstimation wit…
URL: https://github.com/apache/spark/pull/24286
 
 
   ## What changes were proposed in this pull request?
   The upper bound of group-by columns row number is to multiply distinct 
counts of group-by columns. However, column with only null value will cause the 
output row number to be 0 which is incorrect.
   Ex:
   col1 (distinct: 2, rowCount 2)
   col2 (distinct: 0, rowCount 2)
   => group by col1, col2
   Actual: output rows: 0
   Expected: output rows: 2
   
   ## How was this patch tested?
   According unit test has been added, plus manual test has been done in our 
tpcds benchmark environement.

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