cloud-fan commented on issue #25902: [SPARK-29213][SQL] Make it consistent when 
get notnull output and generate null checks in FilterExec
URL: https://github.com/apache/spark/pull/25902#issuecomment-534830584
 
 
   @viirya your proposal works, but is a little against the original design 
goal. Think about `IsNotNull(a + b + c + d ..)` and `Substring(a)`.
   
   When codegen `Substring(a)`, with your proposal, we will codegen 
`IsNotNull(a + b + c + d ..)` first, which loads more columns and may cause 
perf regression.
   
   I have a slightly different proposal: when codegen `Substring(a)`, check if 
there is a `IsNotNull(a)` predicate. If there is, codegen it first. If not, and 
`a` is a not-nullable attribute, then generate a `IsNotNull(a)` and codegen it 
first.

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