[GitHub] [spark] beliefer commented on a diff in pull request #42117: [SPARK-44517][SQL] Respect ignorenulls and child's nullability in first

["beliefer (via GitHub)" <gi...@apache.org>]

beliefer commented on code in PR #42117:
URL: https://github.com/apache/spark/pull/42117#discussion_r1273379892


##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/First.scala:
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@@ -60,7 +60,13 @@ case class First(child: Expression, ignoreNulls: Boolean)
     this(child, FirstLast.validateIgnoreNullExpr(ignoreNullsExpr, "first"))
   }
 
-  override def nullable: Boolean = true
+  override def nullable: Boolean = {
+    if (ignoreNulls) {
+      false

Review Comment:
   All the input values are null is possible, e.g. `SELECT first(col) FILTER (col is null)`.



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