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
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@@ -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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