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From GitBox <...@apache.org>
Subject [GitHub] hequn8128 commented on a change in pull request #6521: [FLINK-5315][table] Adding support for distinct operation for table API on DataStream
Date Wed, 08 Aug 2018 11:47:29 GMT
hequn8128 commented on a change in pull request #6521: [FLINK-5315][table] Adding support for
distinct operation for table API on DataStream
URL: https://github.com/apache/flink/pull/6521#discussion_r208549808
 
 

 ##########
 File path: flink-libraries/flink-table/src/main/scala/org/apache/flink/table/expressions/aggregations.scala
 ##########
 @@ -52,12 +62,49 @@ abstract sealed class Aggregation extends Expression {
 
 }
 
+case class DistinctAgg(child: Expression) extends Aggregation {
+
+  override private[flink] def toAggCall(name: String)(implicit relBuilder: RelBuilder): AggCall
= {
+    child.asInstanceOf[Aggregation].toAggCall(name, isDistinct = true)
+  }
+
+  override private[flink] def resultType: TypeInformation[_] = child.resultType
+
+  override private[flink] def validateInput(): ValidationResult = {
+    super.validateInput()
+    child match {
+      case agg: Aggregation =>
+        child.validateInput()
+      case _ =>
+        ValidationFailure(s"Distinct modifier cannot be applied to $child. " +
+          s"It can only be applied to an aggregation expression!")
 
 Review comment:
   It can only be applied to an aggregation expression, for example, 'a.count.distinct which
means COUNT(DISTINCT a).
   Add an example may be more understandable?

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