neilconway opened a new issue, #22531:
URL: https://github.com/apache/datafusion/issues/22531

   ### Is your feature request related to a problem or challenge?
   
   Currently, the `EliminateOuterJoin` rewrite looks for a `Filter` node 
directly above a `Join` node. For most queries, that is the right plan shape to 
look for (because `PushdownFilter` will typically place the filters that are 
useful for outer join elimination directly on top of the relevant `Join` node). 
However, some plans don't follow this shape:
   
   1. Filters on volatile expressions result in a `Projection` node between the 
`Filter` and the `Join`
   2. `OptimizeProjections` might result in placing a `Projection` node between 
the `Filter` and the `Join`
   
   Notably, case #2 appears when optimizing TPC-DS Q49; we currently fail to 
convert three outer joins to inner joins for that reason.
   
   In both cases, we can teach `EliminateOuterJoin` to look for the `Filter` -> 
`Projection` -> `Join` plan shape as well.
   
   ### Describe the solution you'd like
   
   _No response_
   
   ### Describe alternatives you've considered
   
   _No response_
   
   ### Additional context
   
   _No response_


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