gengliangwang commented on a change in pull request #28733:
URL: https://github.com/apache/spark/pull/28733#discussion_r438381247
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File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/predicates.scala
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@@ -198,6 +200,97 @@ trait PredicateHelper {
case e: Unevaluable => false
case e => e.children.forall(canEvaluateWithinJoin)
}
+
+ /**
+ * Convert an expression into conjunctive normal form.
+ * Definition and algorithm:
https://en.wikipedia.org/wiki/Conjunctive_normal_form
+ * CNF can explode exponentially in the size of the input expression when
converting Or clauses.
+ * Use a configuration MAX_CNF_NODE_COUNT to prevent such cases.
+ *
+ * @param condition to be conversed into CNF.
+ * @return If the number of expressions exceeds threshold on converting Or,
return Seq.empty.
+ * If the conversion repeatedly expands nondeterministic
expressions, return Seq.empty.
+ * Otherwise, return the converted result as sequence of disjunctive
expressions.
+ */
+ def conjunctiveNormalForm(condition: Expression): Seq[Expression] = {
Review comment:
well, let me remove the word `Disjunctive` to avoid misunderstanding.
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