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Subject [GitHub] xccui commented on a change in pull request #6407: [FLINK-9877][docs] Add documentation page for different datastream joins
Date Wed, 25 Jul 2018 17:34:15 GMT
xccui commented on a change in pull request #6407: [FLINK-9877][docs] Add documentation page
for different datastream joins
URL: https://github.com/apache/flink/pull/6407#discussion_r205180168
 
 

 ##########
 File path: docs/dev/stream/operators/joining.md
 ##########
 @@ -0,0 +1,286 @@
+---
+title: "Joining"
+nav-id: streaming_joins
+nav-show_overview: true
+nav-parent_id: streaming
+nav-pos: 10
+---
+<!--
+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.
+-->
+
+* toc
+{:toc}
+
+# Window Join
+A window join will join the elements of two streams that share a common key and lie in the
same window. These windows can be defined by using a [window assigner]({{ site.baseurl}}/dev/stream/operators/windows.html#window-assigners)
and are evaluated on a union of both streams. This is especially important for session window
joins, which will be demonstrated below.
+
+The joined elements are then passed to a user-defined `JoinFunction` or `FlatJoinFunction`
where the user can perform transformations on the joined elements.
+
+The general usage always looks like the followning:
+
+```java
+stream.join(otherStream)
+    .where(<KeySelector>)
+    .equalTo(<KeySelector>)
+    .window(<WindowAssigner>)
+    .apply(<JoinFunction>)
+```
+
+Some notes on semantics:
 
 Review comment:
   Replace these notes with an explanation of the codes above.

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