huaxingao commented on a change in pull request #27297: [SPARK-30588][DOC] Document CLUSTER BY Clause of SELECT statement in SQL Reference. URL: https://github.com/apache/spark/pull/27297#discussion_r368768177
########## File path: docs/sql-ref-syntax-qry-select-clusterby.md ########## @@ -0,0 +1,86 @@ +--- +layout: global +title: CLUSTER BY Clause +displayTitle: CLUSTER BY Clause +license: | + 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. +--- +The <code>CLUSTER BY</code> clause is used to first repartition the data based +on the input expressions and then sort the data within each partition. This is +is semantically equivalent to performing <code>DISTRIBUTE BY</code> followed by +<code>SORT BY</code>. This cause only ensures that the resultant rows are +sorted within each partition and does not guarantee total ordering of output, + +### Syntax +{% highlight sql %} +CLUSTER BY { expression [ , ...] } +{% endhighlight %} + +### Parameters +<dl> + <dt><code><em>expression</em></code></dt> + <dd> + Specifies combination of one or more values, operators and SQL functions that results in a value. + </dd> +</dl> + +### Examples +{% highlight sql %} +CREATE TABLE person (name STRING, age INT); +INSERT INTO person VALUES ('Zen Hui', 25), + ('Anil B', 18), + ('Shone S', 16), + ('Mike A', 25), + ('John A', 18), + ('Jack N', 16); +-- Reduce the number of shuffle partitions to 2 to illustrate the behaviour of `CLUSTER BY`. +-- Its easier to see the clustering and sorting behaviour with less number of partitions. +SET spark.sql.shuffle.partitions = 2; + +-- Select the rows with no ordering. Please note that without any sort directive, the results +-- of the query is not deterministic. Its included here to show the difference in behaviour Review comment: ```results of the query is``` -> ```result of the query is```??? ```Its``` -> ```It's```? ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to 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 --------------------------------------------------------------------- To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org For additional commands, e-mail: reviews-h...@spark.apache.org
