[GitHub] [spark] arkguil commented on issue #22696: [SPARK-25708][SQL] HAVING without GROUP BY means global aggregate

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arkguil commented on issue #22696: [SPARK-25708][SQL] HAVING without GROUP BY means global aggregate
URL: https://github.com/apache/spark/pull/22696#issuecomment-490184967
 
 
   @cloud-fan / @gatorsmile , just stumbled on this while investigating an issue with a query while migrating to 2.4...
   
   Seems like the fix over simplified the original intent. It should be totally ok to do something like 
   
   `select id from range(10) having id > 5`
   
   Having is applied on the result of `select id from range(10)`, and since id is in the resultset, this should not fail with `grouping expressions sequence is empty, and '`id`' is not an aggregate function`.
   
   The previous SQL should be interpreted as 
   
   `select id from range(10) group by id having id > 5`
   
   Which is what the previous plan was doing... This is easier to see when using a window function:
   
   `select id, max(id) over () as `max_id` from range(10) where id > 5 having max_id = id`
   
   The window will be generated then the filter applied on the result. You can't apply a where on `max_id` since it is only available after `select id, max(id) over () as `max_id` from range(10) where id > 5` is executed.
   
   Can you explain what this change fixes exactly?
   
   

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