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https://issues.apache.org/jira/browse/FLINK-5956?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15895993#comment-15895993
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ASF GitHub Bot commented on FLINK-5956:
---------------------------------------
Github user shaoxuan-wang commented on a diff in the pull request:
https://github.com/apache/flink/pull/3470#discussion_r104301092
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/table/functions/aggfunctions/MaxAggFunctionWithRetract.scala
---
@@ -0,0 +1,205 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.flink.table.functions.aggfunctions
+
+import java.math.BigDecimal
+import java.util.{HashMap => JHashMap, List => JList}
+
+import org.apache.flink.api.common.typeinfo.{BasicTypeInfo,
TypeInformation}
+import org.apache.flink.api.java.tuple.{Tuple3 => JTuple3}
+import org.apache.flink.api.java.typeutils.{MapTypeInfo, TupleTypeInfo}
+import org.apache.flink.table.api.TableException
+import org.apache.flink.table.functions.{Accumulator, AggregateFunction}
+
+/** The initial accumulator for Max with retraction aggregate function */
+class MaxWithRetractAccumulator[T] extends JTuple3[T, Long, JHashMap[T,
Long]] with Accumulator
+
+/**
+ * Base class for built-in Max with retraction aggregate function
+ *
+ * @tparam T the type for the aggregation result
+ */
+abstract class MaxWithRetractAggFunction[T](implicit ord: Ordering[T])
extends AggregateFunction[T] {
+
+ override def createAccumulator(): Accumulator = {
+ val acc = new MaxWithRetractAccumulator[T]
+ acc.f0 = getInitValue //max
+ acc.f1 = 0L //total count
+ acc.f2 = new JHashMap[T, Long]() //store the count for each value
--- End diff --
yes, the idea is borrowed from bucket sort, I think this should be the
right dataStructure for max, min, and even medium.
> Add retract method into the aggregateFunction
> ---------------------------------------------
>
> Key: FLINK-5956
> URL: https://issues.apache.org/jira/browse/FLINK-5956
> Project: Flink
> Issue Type: Sub-task
> Components: Table API & SQL
> Reporter: Shaoxuan Wang
> Assignee: Shaoxuan Wang
>
> Retraction method is help for processing updated message. It will also very
> helpful for window Aggregation. This PR will first add retraction methods
> into the aggregateFunctions, such that on-going over window Aggregation can
> get benefit from it.
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