liukun4515 commented on issue #1342:
URL: 
https://github.com/apache/arrow-datafusion/issues/1342#issuecomment-974648662


   > ote this optimization is only valid prior to any OUTER joins
   
   The idea is from [is null 
optimize](https://dev.mysql.com/doc/refman/8.0/en/is-null-optimization.html).
   I think the `is null` optimization has no side effect if the column has `not 
null` constraint.
   But the `is not null` optimization should be checked with more cases, I will 
do it in the followup pull request.


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