[GitHub] [spark] peter-toth commented on a change in pull request #24495: [SPARK-27604][SQL] Enhance constant propagation to constraint propagation

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peter-toth commented on a change in pull request #24495: [SPARK-27604][SQL] Enhance constant propagation to constraint propagation
URL: https://github.com/apache/spark/pull/24495#discussion_r281165606
 
 

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 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
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 @@ -55,100 +55,24 @@ object ConstantFolding extends Rule[LogicalPlan] {
 }
 
 /**
- * Substitutes [[Attribute Attributes]] which can be statically evaluated with their corresponding
- * value in conjunctive [[Expression Expressions]]
+ * Substitutes expressions which can be statically narrowed by constrains.
  * eg.
  * {{{
- *   SELECT * FROM table WHERE i = 5 AND j = i + 3
- *   ==>  SELECT * FROM table WHERE i = 5 AND j = 8
+ *   SELECT * FROM table WHERE i = 5 AND j = i + 3     => SELECT * FROM table WHERE i = 5 AND j = 8
+ *   SELECT * FROM table WHERE i <= 5 AND i = 5        => SELECT * FROM table WHERE i = 5
 
 Review comment:
   I separated the 2 rules. I added some improvement to the `ConstantPropagation' and created a new 'FilterReduction`.

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