fhueske commented on a change in pull request #6741: [FLINK-9712][table,docs] Document processing time Temporal Table Joins URL: https://github.com/apache/flink/pull/6741#discussion_r221982954
########## File path: docs/dev/table/streaming/joins.md ########## @@ -0,0 +1,104 @@ +--- +title: "Joins in Continuous Queries" +nav-parent_id: streaming_tableapi +nav-pos: 3 +--- +<!-- +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. +--> + +When we have two tables that we want to connect such operation can usually be expressed via some kind of join. +In batch processing joins can be efficiently executed, since we are working on a bounded completed data sets. +In stream processing things are a little bit more complicated, +especially when it comes to the issue how to handle that data can change over time. +Because of that, there are a couple of ways to actually perform the join using either Table API or SQL. + +For more information regarding the syntax please check the Joins sections in [Table API](../tableApi.html#joins) and [SQL](../sql.html#joins). + +* This will be replaced by the TOC +{:toc} + +Regular Joins +------------- + +This is the most basic case in which any new records or changes to either side of the join input are visible +and are affecting the whole join result. +For example, if there is a new record on the left side, +it will be joined with all of the previous and future records on the other side. + +These semantics have an important implication: +it requires to keep both sides of the join input in the state indefinitely +and resource usage will grow indefinitely as well, +if one or both input tables are continuously growing. + +Example: +{% highlight sql %} +SELECT * FROM Orders +INNER JOIN Product +ON Orders.productId = Product.id +{% endhighlight %} + +Time-windowed Joins +------------------- + +A time-windowed join is defined by a join predicate, +that checks if [the time attributes](time_attributes.html) of the input records are within a time-window. +Since time attributes are quasi-monontic increasing, +Flink can remove old values from the state without affecting the correctness of the result. + +Example: +{% highlight sql %} +SELECT * +FROM + Orders o, + Shipments s +WHERE o.id = s.orderId AND + o.ordertime BETWEEN s.shiptime - INTERVAL '4' HOUR AND s.shiptime +{% endhighlight %} + +Join with a Temporal Table +-------------------------- + +A Temporal Table Join joins an append-only table (left input/probe side) with a [Temporal Tables](temporal_tables.html) (right input/build side), Review comment: "A join with a Temporal Table joins ..." ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services
