[GitHub] [spark] viirya commented on a change in pull request #33930: [SPARK-36665][SQL] Add more Not operator simplifications

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viirya commented on a change in pull request #33930:
URL: https://github.com/apache/spark/pull/33930#discussion_r707824426



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File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
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@@ -288,8 +288,24 @@ object OptimizeIn extends Rule[LogicalPlan] {
  * 2. Eliminates / extracts common factors.
  * 3. Merge same expressions
  * 4. Removes `Not` operator.
+ * 5. Move/Push `Not` operator if it's beneficial.
  */
 object BooleanSimplification extends Rule[LogicalPlan] with PredicateHelper {
+  // Given argument x, return true if expression Not(x) can be simplified
+  // E.g. let x == Not(y), then canSimplifyNot(x) == true because Not(x) == Not(Not(y)) == y
+  // For the case of x = EqualTo(a, b), recursively check each child expression
+  // Extra nullable check is required for EqualNullSafe because
+  // Not(EqualNullSafe(x, null)) is different from EqualNullSafe(x, Not(null))
+  private def canSimplifyNot(x: Expression): Boolean = x match {

Review comment:
       Does `canSimplifyNot` returning true for an expression `x` means that `Not(x)` can be optimized later to remove `Not`?




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