[GitHub] [spark] gengliangwang commented on a change in pull request #28805: [SPARK-28169][SQL] Convert scan predicate condition to CNF

[GitBox <gi...@apache.org>]

gengliangwang commented on a change in pull request #28805:
URL: https://github.com/apache/spark/pull/28805#discussion_r448143683



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File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/predicates.scala
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@@ -249,8 +251,36 @@ trait PredicateHelper extends Logging {
     resultStack.top
   }
 
-  private def groupExpressionsByQualifier(expressions: Seq[Expression]): Seq[Expression] = {
-    expressions.groupBy(_.references.map(_.qualifier)).map(_._2.reduceLeft(And)).toSeq
+  /**
+   * Convert an expression to conjunctive normal form when pushing predicates through Join,
+   * when expand predicates, we can group by the qualifier avoiding generate unnecessary
+   * expression to control the length of final result since there are multiple tables.
+   *
+   * @param condition condition need to be converted
+   * @return the CNF result as sequence of disjunctive expressions. If the number of expressions
+   *         exceeds threshold on converting `Or`, `Seq.empty` is returned.
+   */
+  def conjunctiveNormalFormAndGroupExpsByQualifier(condition: Expression): Seq[Expression] = {

Review comment:
       On second thought, the method name `conjunctiveNormalFormAndGroupExpsByQualifier` is too long and the `And` is weird.
   How about changing to `CNFWithGroupExpressionsByQualifier`?




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