[jira] [Commented] (FLINK-6465) support FIRST_VALUE on Table API & SQL

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-6465?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16154583#comment-16154583 ] 

ASF GitHub Bot commented on FLINK-6465:
---------------------------------------

Github user sunjincheng121 commented on a diff in the pull request:

    https://github.com/apache/flink/pull/4556#discussion_r137142537
  
    --- Diff: flink-libraries/flink-table/src/main/scala/org/apache/flink/table/functions/aggfunctions/FirstValueAggFunctionWithRetract.scala ---
    @@ -0,0 +1,121 @@
    +/*
    + * 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.{ArrayList => JArray, List => JList}
    +
    +import org.apache.flink.api.common.typeinfo.{BasicTypeInfo, TypeInformation}
    +import org.apache.flink.api.java.tuple.{Tuple1 => JTuple1}
    +import org.apache.flink.api.java.typeutils.TupleTypeInfo
    +import org.apache.flink.table.functions.AggregateFunction
    +
    +/** The initial accumulator for first value with retraction aggregate function */
    +class FirstValueWithRetractAccumulator[T] extends JTuple1[JList[T]]
    --- End diff --
    
     FLINK-7206 is done, I'll  using `DataView` for improve the implementation.


> 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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