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_r221994819
########## File path: docs/dev/table/streaming/temporal_tables.md ########## @@ -0,0 +1,286 @@ +--- +title: "Temporal Tables" +nav-parent_id: streaming_tableapi +nav-pos: 4 +--- +<!-- +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. +--> + +Temporal Tables represent a concept of a table that changes over time. +Flink can keep track of those changes and allows for accessing the table's content at a certain point in time within a query + +* This will be replaced by the TOC +{:toc} + +Motivation +---------- + +Let's assume that we have the following tables. + +{% highlight sql %} +SELECT * FROM Orders; + +rowtime amount currency +======= ====== ========= +10:15 2 Euro +10:30 1 US Dollar +10:32 50 Yen +10:52 3 Euro +11:04 5 US Dollar +{% endhighlight %} + +`Orders` is an append-only table that represents payments for given `amount` and given `currency`. +For example at `10:15` there was an order for an amount of `2 Euro`. + +{% highlight sql %} +SELECT * FROM RatesHistory; + +rowtime currency rate +======= ======== ====== +09:00 US Dollar 102 +09:00 Euro 114 +09:00 Yen 1 +10:45 Euro 116 +11:15 Euro 119 +{% endhighlight %} + +`RatesHistory` represents an ever changing append-only stream of currency exchange rates, with respect to `Yen` (which has a rate of `1`). +For example exchange rate for a period from `09:00` to `10:45` of `Euro` to `Yen` was `114`. +From `10:45` to `11:15` it was `116`. + +Task is now to calculate a value of all of the `Orders` converted to common currency (`Yen`). Review comment: We can just use the example that we would like to have all current rates at `10:58`. Add the SQL query that would be necessary to compute this from `RatesHistory` to precisely define the semantics? ---------------------------------------------------------------- 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
