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https://issues.apache.org/jira/browse/FLINK-6465?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16179246#comment-16179246
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ASF GitHub Bot commented on FLINK-6465:
---------------------------------------
Github user haohui commented on a diff in the pull request:
https://github.com/apache/flink/pull/4556#discussion_r140824819
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/table/functions/aggfunctions/FirstValueAggFunctionWithRetract.scala
---
@@ -0,0 +1,129 @@
+/*
+ * 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 org.apache.flink.api.common.typeinfo.TypeInformation
+import org.apache.flink.table.api.dataview.{ListView, MapView}
+import org.apache.flink.table.functions.AggregateFunction
+
+/** The initial accumulator for first value with retraction aggregate
function */
+class FirstValueWithRetractAccumulator[T] {
+ var data: ListView[T] = _
+ var retractedData: MapView[T, Byte] = _
+
+ override def equals(obj: scala.Any): Boolean = {
+ if (obj.isInstanceOf[FirstValueWithRetractAccumulator[T]]) {
+ val target = obj.asInstanceOf[FirstValueWithRetractAccumulator[T]]
+ if (target.data.equals(this.data) &&
target.retractedData.equals(this.retractedData)) {
+ return true
+ }
+ }
+ false
+ }
+}
+
+/**
+ * Base class for built-in first value with retraction aggregate function
+ *
+ * @tparam T the type for the aggregation result
+ */
+abstract class FirstValueWithRetractAggFunction[T]
+ extends AggregateFunction[T, FirstValueWithRetractAccumulator[T]] {
+
+ override def createAccumulator(): FirstValueWithRetractAccumulator[T] = {
+ val acc = new FirstValueWithRetractAccumulator[T]
+ acc.data = new ListView[T]
+ acc.retractedData = new MapView[T, Byte]
+ acc
+ }
+
+ def accumulate(acc: FirstValueWithRetractAccumulator[T], value: Any):
Unit = {
+ if (null != value) {
+ val v = value.asInstanceOf[T]
+ acc.data.add(v)
+ }
+ }
+
+ def retract(acc: FirstValueWithRetractAccumulator[T], value: Any): Unit
= {
--- End diff --
It seems that we can do better than having two copies of state here.
It might make sense to extend the ListView interface or to introduce a
TreeMap like view.
> support FIRST_VALUE on Table API & SQL
> --------------------------------------
>
> Key: FLINK-6465
> URL: https://issues.apache.org/jira/browse/FLINK-6465
> Project: Flink
> Issue Type: Sub-task
> Components: Table API & SQL
> Reporter: Hequn Cheng
> Assignee: sunjincheng
>
> {{FIRST_VALUE}} is a OVER WINDOW function. In this JIRA. will add
> {{FIRST_VALUE}} function support on TableAPI & SQL.
> *Syntax:*
> FIRST_VALUE ( [scalar_expression ] )
> OVER ( [ partition_by_clause ] order_by_clause [ rows_range_clause ] )
> [About OVER
> WINDOWS|https://ci.apache.org/projects/flink/flink-docs-release-1.4/dev/table/tableApi.html#over-windows]
> scalar_expression
> Is the value to be returned. scalar_expression can be a column, or other
> arbitrary expression that results in a single value. Other analytic functions
> are not permitted.
> *NOTE:*
> * {{FIRST_VALUE}} if used for OVER WINDOW, e.g.:
> {code}
> SELECT A, B, FIRST_VALUE(C) OVER (ORDER BY E) AS firstValue FROM tab
> {code}
> * OVER WINDOW's retraction is expensive(currently not supported yet), and
> this JIRA. does not implement Retract logic of {{FIRST_VALUE}}.
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