maropu edited a comment on issue #27233: [SPARK-29701][SQL] Correct behaviours of group analytical queries when empty input given URL: https://github.com/apache/spark/pull/27233#issuecomment-577457202 > it seems weird to be to return count of 0 when you have no grouping @tgravescs we need more checks and could you show us these results (MS SQL server and Oracle) here? IIUC this is a known behaviour in the relational database theory; ``` Another property that is hard to understand at first is how GROUP BY works on an empty set. Consider this query: SELECT SUM(x) FROM Empty; which returns a result table with a single NULL. ``` cited from `Joe Celko's Data and Databases: Concepts in Practice`, p79-80, http://www.library.uc.edu.kh/userfiles/pdf/35.Joe%20Celko's%20Data%20and%20Databases%20Concepts%20in%20Practice.pdf
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