pengbo commented on issue #24286: [SPARK-27351][SQL] Wrong outputRows estimation after AggregateEstimation wit… URL: https://github.com/apache/spark/pull/24286#issuecomment-482087006 > when the column is all null? distinct would return 0 rows? then a groupBy on that column still returns 1 grouping for that column? @srowen Thanks for your comment. Yes, that's actually what's happening. Currently if one group by col is all null, the group by output rows estimation will be always 0. Please recheck the example I provided, feel free to ask if you need more information.
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