Github user sunjincheng121 commented on a diff in the pull request: https://github.com/apache/flink/pull/4379#discussion_r128658053 --- Diff: flink-libraries/flink-table/src/main/scala/org/apache/flink/table/functions/AggregateFunction.scala --- @@ -136,8 +137,26 @@ abstract class AggregateFunction[T, ACC] extends UserDefinedFunction { */ def getValue(accumulator: ACC): T - /** - * whether this aggregate only used in OVER clause + /** + * Returns true if this AggregateFunction can only be applied in an OVER window. + * + * @return true if the AggregateFunction requires an OVER window, false otherwise. */ def requiresOver: Boolean = false + + /** + * Returns the TypeInformation for the result of the AggregateFunction. + * + * @return The TypeInformation of the result of the AggregateFunction or null if the result type + * should be automatically inferred. + */ + def getResultType: TypeInformation[T] = null + + /** + * Returns the TypeInformation for the accumulator of the AggregateFunction. --- End diff -- ` Returns the TypeInformation for` -> ` Returns of TypeInformation for`
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