Github user liancheng commented on a diff in the pull request:
https://github.com/apache/spark/pull/8200#discussion_r37075991
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/predicates.scala
---
@@ -59,6 +59,30 @@ trait PredicateHelper {
}
}
+ /**
+ * Convert an expression into its conjunctive normal form (CNF), i.e.
AND of ORs.
+ * For example, a && b || c is normalized to (a || c) && (b || c) by
this method.
+ *
+ * Refer to https://en.wikipedia.org/wiki/Conjunctive_normal_form for
more information
+ */
+ protected def cnfNormalization(condition: Expression): Expression = {
+ condition.transformUp {
+ case or: Or => pushOrToBottom(or)
+ }
+ }
+
+ private def pushOrToBottom(condition: Expression): Expression = {
+ condition match {
+ case Or(left, right) => (left, right) match {
+ case (And(ll, lr), r) =>
+ And(pushOrToBottom(Or(ll, r)), pushOrToBottom(Or(lr, r)))
+ case (l, And(rl, rr)) =>
+ And(pushOrToBottom(Or(l, rl)), pushOrToBottom(Or(l, rr)))
+ case (l, r) => Or(l, r)
+ }
+ }
+ }
--- End diff --
The following version may be questionably more readable:
```scala
private def pushOrToBottom(condition: Expression): Expression = {
condition match {
case Or(And(innerLhs, innerRhs), rhs) =>
And(pushOrToBottom(Or(innerLhs, rhs)), pushOrToBottom(Or(innerRhs,
rhs)))
case Or(lhs, And(innerLhs, innerRhs)) =>
And(pushOrToBottom(Or(lhs, innerLhs)), pushOrToBottom(Or(lhs,
innerRhs)))
case _ => condition
}
}
```
Shall we also cover cases like `Not(Or(x, y))` => `And(Not(x), Not(y))`
here?
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