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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-5698) Add NestedFieldsProjectableTableSource interface
Date Sat, 18 Feb 2017 07:52:44 GMT

    [ https://issues.apache.org/jira/browse/FLINK-5698?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15873044#comment-15873044
] 

ASF GitHub Bot commented on FLINK-5698:
---------------------------------------

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

    https://github.com/apache/flink/pull/3269#discussion_r101887737
  
    --- Diff: flink-libraries/flink-table/src/main/scala/org/apache/flink/table/sources/NestedFieldsProjectableTableSource.scala
---
    @@ -0,0 +1,39 @@
    +/*
    + * 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.sources
    +
    +/**
    +  * Adds support for projection push-down to a [[TableSource]] with nested fields.
    +  * A [[TableSource]] extending this interface is able
    +  * to project the nested fields of the return table.
    +  *
    +  * @tparam T The return type of the [[NestedFieldsProjectableTableSource]].
    +  */
    +trait NestedFieldsProjectableTableSource[T] extends ProjectableTableSource[T] {
    +
    +  /**
    +    * Creates a copy of the [[NestedFieldsProjectableTableSource]]
    +    * that projects its output on the specified nested fields.
    +    *
    +    * @param fields The indexes of the fields to return.
    +    * @return A copy of the [[NestedFieldsProjectableTableSource]] that projects its
output.
    +    */
    +  def projectNestedFields(fields: Array[String]): NestedFieldsProjectableTableSource[T]
    --- End diff --
    
    @fhueske , I'm fine with this, but have some questions to make sure I understand right.
    
    Say we have a complex table schema as shown below:
    
    ```
    id,
    student<school<city, tuition>, age, name>,
    teacher<age, name>
    ```
    
    The `id, student, teacher` is the first level column, and `student` have a nested `school,
age, name` columns, and `school` has a nested `city, tuition` columns also.
    
    If a user select `id, student.school.city, student.age, teacher`, what the actual arguments
should be?
    `field = [0, 1, 2]` and `nestedFields = `[ [], ["school.city", "age"], ["age", "name"]
]` ? 



> Add NestedFieldsProjectableTableSource interface
> ------------------------------------------------
>
>                 Key: FLINK-5698
>                 URL: https://issues.apache.org/jira/browse/FLINK-5698
>             Project: Flink
>          Issue Type: New Feature
>          Components: Table API & SQL
>            Reporter: Anton Solovev
>            Assignee: Anton Solovev
>
> Add a NestedFieldsProjectableTableSource interface for some TableSource implementation
that support nesting projection push-down.
> The interface could look as follows
> {code}
> def trait NestedFieldsProjectableTableSource {
>   def projectNestedFields(fields: Array[String]): NestedFieldsProjectableTableSource[T]
> }
> {code}
> This interface works together with ProjectableTableSource 



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