[GitHub] [pinot] walterddr commented on pull request #7678: Fixing DISTINCT with AS function

[GitBox <gi...@apache.org>]

walterddr commented on pull request #7678:
URL: https://github.com/apache/pinot/pull/7678#issuecomment-958456613


   i think the fundamental problem here is that `distinct` is modeled as a function. where distinct is actually a selectNode attribute in calcite see: https://github.com/apache/calcite/blob/82dd78a14f6aef2eeec2f9c94978d04b4acc5359/core/src/main/java/org/apache/calcite/sql/SqlSelect.java#L140-L142.
   
   For example as @Jackie-Jiang mentioned: 
   ```
   select CAST(runs AS string) as a, CAST(num AS int) as b from baseballStats GROUP BY 1, 2
   ```
   actually should be modified as:
   ```
   SELECT DISTINCT -- notice that DISTINCT is a modifier of SELECT, not the 2 projection elements.
     CAST(runs AS string) as a, 
     CAST(num AS int) as b
   FROM
     baseballStats 
   GROUP BY 1, 2
   ```
   see calcite syntactic note:
   ```
   select:
         SELECT [ hintComment ] [ STREAM ] [ ALL | DISTINCT ]
             { * | projectItem [, projectItem ]* }
         FROM tableExpression
         [ WHERE booleanExpression ]
         [ GROUP BY { groupItem [, groupItem ]* } ]
         [ HAVING booleanExpression ]
         [ WINDOW windowName AS windowSpec [, windowName AS windowSpec ]* ]
   ```
   DISTINCT is a modifier of the SELECT, not the underlying projectItems. 


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