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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-6465) support FIRST_VALUE on Table API & SQL
Date Mon, 25 Sep 2017 16:19:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-6465?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16179246#comment-16179246
] 

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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