[GitHub] [incubator-druid] clintropolis commented on issue #8013: Fix ExpressionVirtualColumn capabilities; fix groupBy's improper uses of StorageAdapter#getColumnCapabilities.

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clintropolis commented on issue #8013: Fix ExpressionVirtualColumn capabilities; fix groupBy's improper uses of StorageAdapter#getColumnCapabilities.
URL: https://github.com/apache/incubator-druid/pull/8013#issuecomment-508853701
 
 
   >I pushed a fix for the ExpressionVirtualColumn issue and updated the top comment. In this fix I just set it to always be "true". This isn't ideal, since it means singly-valued optimizations won't work on top of it, but I didn't see an easy way for the ExpressionVirtualColumn to determine upfront if it will be singly-valued or not. I think this should be possible in the future as we add more upfront type info to the expression system, so I added a comment saying as much.
   
   :+1: I think this makes sense for now, I will follow this up with a fix to allow us to determine when a single input column will produce an scalar or array output so we can have this optimization again where possible.

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