[GitHub] [flink] knaufk commented on a change in pull request #8903: [FLINK-12747][docs] Getting Started - Table API Example Walkthrough

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knaufk commented on a change in pull request #8903: [FLINK-12747][docs] Getting Started - Table API Example Walkthrough
URL: https://github.com/apache/flink/pull/8903#discussion_r298005605
 
 

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 File path: docs/getting-started/tutorials/table_api.md
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+---
+title: "Table API"
+nav-id: tableapitutorials
+nav-title: 'Table API'
+nav-parent_id: apitutorials
+nav-pos: 1
+---
+<!--
+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.
+-->
+
+Apache Flink offers a Table API as a unified, relational API for batch and stream processing, i.e., queries are executed with the same semantics on unbounded, real-time streams or bounded, recorded streams and produce the same results.
+The Table API in Flink is commonly used to ease the definition of data analytics, data pipelining, and ETL applications.
+
+* This will be replaced by the TOC
+{:toc}
+
+## What Are We Building? 
+
+In this tutorial, we'll show how to build a continuous ETL pipeline for tracking financial transactions by account over time.
+We will start by building our report as a nightly batch job, and then migrate to a streaming pipeline to see how batch is just a special case of streaming. 
+
+## Prerequisites
+
+We'll assume that you have some familiarity with Java or Scala, but you should be able to follow along even if you're coming from a different programming language.
+We'll also assume that you're familiar with basic relational concepts such as `SELECT` and `GROUP BY` clauses. 
+
+If you want to follow along you will require a computer with: 
+
+* Java 8 
+* Maven 
+
+## Help, I’m Stuck! 
+
+If you get stuck, check out the [community support resources](https://flink.apache.org/community.html).
+In particular, Apache Flink's [user mailing list](https://flink.apache.org/community.html#mailing-lists) is consistently ranked as one of the most active of any Apache project and a great way to get help quickly. 
+
+## Setting up a Maven Project
+
+We are going to use a Flink Maven Archetype for creating our project structure.
+
+{% highlight bash %}
+$ mvn archetype:generate \
+    -DarchetypeGroupId=org.apache.flink \
+    -DarchetypeArtifactId=flink-walkthrough-table \{% unless site.is_stable %}
+    -DarchetypeCatalog=https://repository.apache.org/content/repositories/snapshots/ \{% endunless %}
+    -DarchetypeVersion={{ site.version }} \
+    -DgroupId=spend-report \
+    -DartifactId=spend-report \
+    -Dversion=0.1 \
+    -Dpackage=spendreport \
+    -DinteractiveMode=false
+{% endhighlight %}
+
+{% unless site.is_stable %}
+<p style="border-radius: 5px; padding: 5px" class="bg-danger">
+    <b>Note</b>: For Maven 3.0 or higher, it is no longer possible to specify the repository (-DarchetypeCatalog) via the commandline. If you wish to use the snapshot repository, you need to add a repository entry to your settings.xml. For details about this change, please refer to <a href="http://maven.apache.org/archetype/maven-archetype-plugin/archetype-repository.html">Maven official document</a>
+</p>
+{% endunless %}
+
+You can edit the `groupId`, `artifactId` and `package` if you like. With the above parameters,
+Maven will create a project with all the dependencies to complete this tutorial.
+After importing the project in your editor you will see a file following code. 
+
+{% highlight java %}
+ExecutionEnvironment env   = ExecutionEnvironment.getExecutionEnvironment();
+BatchTableEnvironment tEnv = BatchTableEnvironment.create(env);
+
+tEnv.registerTableSource("transactions", new TransactionTableSource());
+tEnv.registerTableSink("stdout", new StdOutTableSink());
+tEnv.registerFunction("truncateDateToHour", new TruncateDateToHour());
+
+tEnv
+	.scan("transactions")
+	.insertInto("stdout");
+
+env.execute("Spend Report");
+{% endhighlight %}
+
+Let's break down this code by component. 
+
+## Breaking Down The Code
+
+#### The Execution Environment
+
+The first two lines set up our `ExecutionEnvironment`.
+The execution environment is how we set properties for our deployments, specify whether we are writing a batch or streaming application, and create our sources.
+Here we have chosen to use the batch environment since we are building a periodic batch report.
+We then wrap it in a `BatchTableEnvironment` so to have full access to the Table Api.
+
+{% highlight java %}
+ExecutionEnvironment env   = ExecutionEnvironment.getExecutionEnvironment();
+BatchTableEnvironment tEnv = BatchTableEnvironment.create(env);
+{% endhighlight %}
+
+#### Registering Tables
+
+Next, we register tables that we can use for the input and output of our application. 
+The TableEnvironment maintains a catalog of tables that are registered by name. There are two types of tables, input tables and output tables.
+Input tables can be referenced in Table API and SQL queries and provide input data.
+Output tables can be used to emit the result of a Table API or SQL query to an external system.
+Tables can support batch queries, streaming queries, or both. 
+
+{% highlight java %}
+tEnv.registerTableSource("transactions", new TransactionTableSource());
+tEnv.registerTableSink("stdout", new StdOutTableSink());
+{% endhighlight %}
+
+We register two tables, a `transactions` input table and a `stdout` output table. 
 
 Review comment:
   The naming is a bit inconsistent: 
   * `transactions` is named by its content
   * `stdout` is named by the target system
   We could also change `stdout` to something like `spend_reports`.

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