[GitHub] [druid] imply-cheddar commented on pull request #13922: Refactoring and bug fixes on top of unnest. The allowList now is not passed …

["imply-cheddar (via GitHub)" <gi...@apache.org>]

imply-cheddar commented on PR #13922:
URL: https://github.com/apache/druid/pull/13922#issuecomment-1467236981

   Something I don't understand with this structuring of the code.  When we look at the actions taken in planning and running these queries we get
   
   1) SQL is parsed into parse tree and converted to logical DAG
   2) Logical DAG is optimized such that filters are applied to each side of the UNNEST correlate (i.e. Calcite figures out which filters apply to the unnested column (rhs of the LogicalCorrelate with the Uncollect) and which filters apply to the base query (lhs of the LogicalCorrelate with the Uncollect)
   3) We have rules that push all of the filters that Calcite already figured out for us such that they are above the`LogicalCorrelate`.
   4) We build a native query with the filters all meshed together
   5) The native query then has code that figures out, once again, whether some of the filters can be rewritten to be running against the underlying columns
   
   It seems weird to me that we would explicitly undo the thing that Calcite figured out for us so that we can attempt to re-do it in the native query.
   
   I'd propose that we take a `Filter` object on the `UnnestDatasource`.  The UnnestCursor can pretty easily attempt the re-write and pushdown of that RHS filter and also attach it as a `ValueMatcher` on the read.  This is also seems like a much more natural way to plan the query, no?  
   
   Is there some reason that we have to throw away the work that Calcite already did for us only to redo it?


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