[GitHub] cloud-fan commented on a change in pull request #23867: [SPARK-26965][SQL] Makes ElementAt nullability more precise

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cloud-fan commented on a change in pull request #23867: [SPARK-26965][SQL] Makes ElementAt nullability more precise
URL: https://github.com/apache/spark/pull/23867#discussion_r261498779
 
 

 ##########
 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/complexTypeExtractors.scala
 ##########
 @@ -281,10 +266,50 @@ case class GetArrayItem(child: Expression, ordinal: Expression)
 }
 
 /**
- * Common base class for [[GetMapValue]] and [[ElementAt]].
+ * Common trait for [[GetArrayItem]] and [[ElementAt]].
  */
+trait GetArrayItemUtil {
+
+  /** `Null` is returned for invalid ordinals. */
+  protected def computeNullabilityFromArray(child: Expression, ordinal: Expression): Boolean = {
+    if (ordinal.foldable && !ordinal.nullable) {
+      val intOrdinal = ordinal.eval().asInstanceOf[Number].intValue()
+      child match {
+        case CreateArray(ar) if intOrdinal < ar.length =>
+          ar(intOrdinal).nullable
+        case GetArrayStructFields(CreateArray(elements), field, _, _, _)
+          if intOrdinal < elements.length =>
+          elements(intOrdinal).nullable || field.nullable
+        case _ =>
+          true
+      }
+    } else {
+      true
+    }
+  }
+}
+
+/**
+ * Common trait for [[GetMapValue]] and [[ElementAt]].
+ */
+trait GetMapValueUtil extends BinaryExpression with ImplicitCastInputTypes {
+
+  /** `Null` is returned for invalid ordinals. */
+  protected def computeNullabilityFromMap: Boolean = if (right.foldable && !right.nullable) {
+    val keyObj = right.eval()
+    left match {
+      case m: CreateMap if m.resolved =>
+        m.keys.zip(m.values).filter { case (k, _) => k.foldable && !k.nullable }.find {
+          case (k, _) if k.eval() == keyObj => true
 
 Review comment:
   can we rely on `==`? What if one expression returns unsafe row and the other returns safe row?
   
   I know this is existing code, but after a hindsight maybe it's not worth to linear scan the map entries and just to get the precise nullability.

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