[GitHub] [spark] davidvrba commented on a change in pull request #27231: [SPARK-28478][SQL] Remove redundant null checks

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davidvrba commented on a change in pull request #27231: [SPARK-28478][SQL] Remove redundant null checks
URL: https://github.com/apache/spark/pull/27231#discussion_r376236285
 
 

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 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
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 @@ -434,6 +434,27 @@ object SimplifyConditionals extends Rule[LogicalPlan] with PredicateHelper {
     case _ => false
   }
 
+  /**
+   * Condition for redundant null check based on intolerant expressions.
+   * @param ifNullExpr expression that takes place if checkedExpr is null
+   * @param ifNotNullExpr expression that takes place if checkedExpr is not null
+   * @param checkedExpr expression that is checked for null value
+   */
+  private def isRedundantNullCheck(
+      ifNullExpr: Expression,
+      ifNotNullExpr: Expression,
+      checkedExpr: Expression): Boolean = {
+    val isNullIntolerant = ifNotNullExpr.find { x =>
+      !x.isInstanceOf[NullIntolerant] && x.find(e => e.semanticEquals(checkedExpr)).nonEmpty
 
 Review comment:
   Yeah, `FilterExec.isNullIntolerant(ifNotNullExpr)` is a stronger condition than we need so in case there is null-tolerant expr inside we need to check if the null-checked column is in its subtree. Using the logic from `FilterExec.isNullIntolerant` the function could look like this:
   ```
   def isNullIntolerant(expr: Expression): Boolean = expr match {
     case e: NullIntolerant => e.children.forall(isNullIntolerant)
     case e if e.find(x => x.semanticEquals(checkedExpr)).isEmpty => true
     case _ => false
   }
   ```

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