fhueske 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_r211234086
##########
File path:
flink-libraries/flink-table/src/main/scala/org/apache/flink/table/functions/AggregateFunction.scala
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@@ -136,4 +138,12 @@ abstract class AggregateFunction[T, ACC] extends
UserDefinedFunction {
* accumulator type should be automatically inferred.
*/
def getAccumulatorType: TypeInformation[ACC] = null
+
+ /**
+ * Returns an aggregation function that requires distinct accumulator.
+ * @return distinct aggregate version of the [[AggregateFunction]].
+ */
+ private[flink] def distinct: DistinctAggregateFunction[T, ACC] =
DistinctAggregateFunction(this)
Review comment:
I think it would be better to not change the `AggregateFunction` class. I'd
rather add an implicit conversion to the `expressionDsl` which converts
`AggregateFunction` to `DistinctAggregateFunction` (see below) that has a
`distinct()` method that returns a `DistinctAgg()` expression.
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