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From rxin <...@git.apache.org>
Subject [GitHub] spark pull request: [SPARK-13658][SQL] BooleanSimplification rule ...
Date Mon, 14 Mar 2016 05:55:19 GMT
Github user rxin commented on a diff in the pull request:

    https://github.com/apache/spark/pull/11647#discussion_r55958696
  
    --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala
---
    @@ -598,3 +601,61 @@ abstract class TernaryExpression extends Expression {
         }
       }
     }
    +
    +/**
    + * Rewrites an expression using rules that are guaranteed preserve the result while attempting
    + * to remove cosmetic variations. Deterministic expressions that are `equal` after canonicalization
    + * will always return the same answer given the same input (i.e. false positives should
not be
    + * possible). However, it is possible that two canonical expressions that are not equal
will in fact
    + * return the same answer given any input (i.e. false negatives are possible).
    + *
    + * The following rules are applied:
    + *  - Names and nullability hints for [[org.apache.spark.sql.types.DataType]]s are stripped.
    + *  - Commutative and associative operations ([[Add]] and [[Multiply]]) have their children
ordered
    + *    by `hashCode`.
    +*   - [[EqualTo]] and [[EqualNullSafe]] are reordered by `hashCode`.
    + *  - Other comparisons ([[GreaterThan]], [[LessThan]]) are reversed by `hashCode`.
    + */
    +object Canonicalize extends {
    --- End diff --
    
    fwiw, if you are keeping this class, i think we should just have it in its own file. The
Expression.scala file is getting pretty long.


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