[GitHub] [spark] HyukjinKwon commented on a change in pull request #24182: [SPARK-27246][SQL]scalar subquery with no columns throws exception in spark shell

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HyukjinKwon commented on a change in pull request #24182: [SPARK-27246][SQL]scalar subquery with no columns throws exception in spark shell
URL: https://github.com/apache/spark/pull/24182#discussion_r268469102
 
 

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 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/subquery.scala
 ##########
 @@ -248,7 +248,11 @@ case class ScalarSubquery(
     children: Seq[Expression] = Seq.empty,
     exprId: ExprId = NamedExpression.newExprId)
   extends SubqueryExpression(plan, children, exprId) with Unevaluable {
-  override def dataType: DataType = plan.schema.fields.head.dataType
+  override def dataType: DataType = if (!plan.schema.fields.isEmpty) {
+    plan.schema.fields.head.dataType
+  } else {
+    NullType
 
 Review comment:
   Can we pull out when this can happen? Is it test only issue or dose it happen in an actual end-to-end case?

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