[GitHub] [spark] cloud-fan commented on a change in pull request #27861: [SPARK-30707][SQL]Window function set partitionSpec as order spec when orderSpec is empty

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cloud-fan commented on a change in pull request #27861: [SPARK-30707][SQL]Window function set partitionSpec as order spec when orderSpec is empty
URL: https://github.com/apache/spark/pull/27861#discussion_r390791856
 
 

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 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/parser/AstBuilder.scala
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 @@ -1691,7 +1691,15 @@ class AstBuilder(conf: SQLConf) extends SqlBaseBaseVisitor[AnyRef] with Logging
   override def visitWindowDef(ctx: WindowDefContext): WindowSpecDefinition = withOrigin(ctx) {
     // CLUSTER BY ... | PARTITION BY ... ORDER BY ...
     val partition = ctx.partition.asScala.map(expression)
-    val order = ctx.sortItem.asScala.map(visitSortItem)
+    val order = if (ctx.sortItem.asScala.nonEmpty) {
+      ctx.sortItem.asScala.map(visitSortItem)
+    } else {
+      // Same default behaviors like hive, when order spec is null
 
 Review comment:
   From the ANSI SQL spec: `If WD has no window ordering clause, then the window ordering is implementation-dependent, and all rows are peers.`
   
   I don't think this is a bug fix but rather a new feature. We need to justify it: what's the behavior of other popular SQL systems like presto, snowflake, redshift, etc.? And what's the benefit for end users?

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