[GitHub] [spark] dongjoon-hyun commented on a change in pull request #24495: [SPARK-27604][SQL] Add filter reduction

[GitBox <gi...@apache.org>]

dongjoon-hyun commented on a change in pull request #24495: [SPARK-27604][SQL] Add filter reduction
URL: https://github.com/apache/spark/pull/24495#discussion_r282195808
 
 

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 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
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 @@ -55,99 +55,114 @@ object ConstantFolding extends Rule[LogicalPlan] {
 }
 
 /**
- * Substitutes [[Attribute Attributes]] which can be statically evaluated with their corresponding
+ * Substitutes [[Expression Expressions]] which can be statically evaluated with their corresponding
  * value in conjunctive [[Expression Expressions]]
  * 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             =>  ... WHERE i = 5 AND j = 8
+ *   SELECT * FROM table WHERE abs(i) = 5 AND j <= abs(i) + 3  =>  ... WHERE abs(i) = 5 AND j <= 8
  * }}}
  *
  * Approach used:
- * - Populate a mapping of attribute => constant value by looking at all the equals predicates
- * - Using this mapping, replace occurrence of the attributes with the corresponding constant values
- *   in the AND node.
+ * - Populate a mapping of expression => constant value by looking at all the deterministic equals
+ *   predicates
+ * - Using this mapping, replace occurrence of the expressions with the corresponding constant
+ *   values in the AND node.
  */
 object ConstantPropagation extends Rule[LogicalPlan] with PredicateHelper {
 
 Review comment:
   Since new PR is created, we had better remove this change from this PR.

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