kazuyukitanimura commented on a change in pull request #33930:
URL: https://github.com/apache/spark/pull/33930#discussion_r706584087



##########
File path: 
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
##########
@@ -441,6 +456,25 @@ object BooleanSimplification extends Rule[LogicalPlan] 
with PredicateHelper {
 
       case Not(IsNull(e)) => IsNotNull(e)
       case Not(IsNotNull(e)) => IsNull(e)
+
+      // Move `Not` from one side of `EqualTo`/`EqualNullSafe` to the other 
side if it's beneficial.
+      // E.g. `EqualTo(Not(a), b)` where `b = Not(c)`, it will become
+      // `EqualTo(a, Not(b))` => `EqualTo(a, Not(Not(c)))` => `EqualTo(a, c)`
+      // In addition, `if canSimplifyNot(b)` checks if the optimization can 
converge
+      // that avoids the situation two conditions are returning to each other.
+      case EqualTo(Not(a), b) if canSimplifyNot(b) => EqualTo(a, Not(b))

Review comment:
       We can but the extra checks are a bit redundant because all `Not` 
optimizations are listed above this line of the case match. Do you feel we must 
need the extra checks? @dbtsai 
   It is actually does not matter `a` or `b` gets simplified because 
`canSimplifyNot()` promises it will be simpler than current form.




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