[GitHub] [spark] peter-toth commented on issue #27518: [SPARK-30768][SQL] Constraints should be inferred from inequality attributes

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peter-toth commented on issue #27518: [SPARK-30768][SQL] Constraints should be inferred from inequality attributes
URL: https://github.com/apache/spark/pull/27518#issuecomment-584839346
 
 
   Is the title correct? Isn't what you do here is constant propagation among constraints?
   Obviously it helps with inequalities of attributes, but also helps where you have complex equalities like `select t1.* from SPARK_30768_1 t1 join SPARK_30768_2 t2 on f(t1.c1) = t2.c1 where t1.c1 = 3` (where `f` is a deterministic function).
   
   BTW, I have a PR open to enhance `ConstantPropagation`: https://github.com/apache/spark/pull/24553 where among other enhancements I try to extend propagation of attribute => constant mapping to propagation of deterministic expression => constant mapping. Maybe you could do expression => constant propagation here as well.

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