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spark-instrumented-optimizer/docs/sql-ref-syntax-qry-select-sortby.md
Takeshi Yamamuro 179289f0bf [SPARK-31383][SQL][DOC] Clean up the SQL documents in docs/sql-ref* 
### What changes were proposed in this pull request?

This PR intends to clean up the SQL documents in `doc/sql-ref*`.
Main changes are as follows;

 - Fixes wrong syntaxes and capitalize sub-titles
 - Adds some DDL queries in `Examples` so that users can run examples there
 - Makes query output in `Examples` follows the `Dataset.showString` (right-aligned) format
 - Adds/Removes spaces, Indents, or blank lines to follow the format below;

```
---
license...
---

### Description

Writes what's the syntax is.

### Syntax

{% highlight sql %}
SELECT...
    WHERE... // 4 indents after the second line
    ...
{% endhighlight %}

### Parameters

<dl>

  <dt><code><em>Param Name</em></code></dt>
  <dd>
    Param Description
  </dd>
  ...
</dl>

### Examples

{% highlight sql %}
-- It is better that users are able to execute example queries here.
-- So, we prepare test data in the first section if possible.
CREATE TABLE t (key STRING, value DOUBLE);
INSERT INTO t VALUES
    ('a', 1.0), ('a', 2.0), ('b', 3.0), ('c', 4.0);

-- query output has 2 indents and it follows the `Dataset.showString`
-- format (right-aligned).
SELECT * FROM t;
  +---+-----+
  |key|value|
  +---+-----+
  |  a|  1.0|
  |  a|  2.0|
  |  b|  3.0|
  |  c|  4.0|
  +---+-----+

-- Query statements after the second line have 4 indents.
SELECT key, SUM(value)
    FROM t
    GROUP BY key;
  +---+----------+
  |key|sum(value)|
  +---+----------+
  |  c|       4.0|
  |  b|       3.0|
  |  a|       3.0|
  +---+----------+
...
{% endhighlight %}

### Related Statements

 * [XXX](xxx.html)
 * ...
```

### Why are the changes needed?

The most changes of this PR are pretty minor, but I think the consistent formats/rules to write documents are important for long-term maintenance in our community

### Does this PR introduce any user-facing change?

Yes.

### How was this patch tested?

Manually checked.

Closes #28151 from maropu/MakeRightAligned.

Authored-by: Takeshi Yamamuro <yamamuro@apache.org>
Signed-off-by: Sean Owen <srowen@gmail.com>
2020-04-12 23:40:36 -05:00

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---
layout: global
title: SORT BY Clause
displayTitle: SORT 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.
---
### Description
The <code>SORT BY</code> clause is used to return the result rows sorted
within each partition in the user specified order. When there is more than one partition
<code>SORT BY</code> may return result that is partially ordered. This is different
than [ORDER BY](sql-ref-syntax-qry-select-orderby.html) clause which guarantees a
total order of the output.
### Syntax
{% highlight sql %}
SORT BY { expression [ sort_direction | nulls_sort_order ] [ , ... ] }
{% endhighlight %}
### Parameters
<dl>
<dt><code><em>SORT BY</em></code></dt>
<dd>
Specifies a comma-separated list of expressions along with optional parameters <code>sort_direction</code>
and <code>nulls_sort_order</code> which are used to sort the rows within each partition.
</dd>
<dt><code><em>sort_direction</em></code></dt>
<dd>
Optionally specifies whether to sort the rows in ascending or descending
order. The valid values for the sort direction are <code>ASC</code> for ascending
and <code>DESC</code> for descending. If sort direction is not explicitly specified, then by default
rows are sorted ascending. <br><br>
<b>Syntax:</b>
<code>
[ ASC | DESC ]
</code>
</dd>
<dt><code><em>nulls_sort_order</em></code></dt>
<dd>
Optionally specifies whether NULL values are returned before/after non-NULL values. If
<code>null_sort_order</code> is not specified, then NULLs sort first if sort order is
<code>ASC</code> and NULLS sort last if sort order is <code>DESC</code>.<br><br>
<ol>
<li> If <code>NULLS FIRST</code> is specified, then NULL values are returned first
regardless of the sort order.</li>
<li>If <code>NULLS LAST</code> is specified, then NULL values are returned last regardless of
the sort order. </li>
</ol><br>
<b>Syntax:</b>
<code>
[ NULLS { FIRST | LAST } ]
</code>
</dd>
</dl>
### Examples
{% highlight sql %}
CREATE TABLE person (zip_code INT, name STRING, age INT);
INSERT INTO person VALUES
(94588, 'Zen Hui', 50),
(94588, 'Dan Li', 18),
(94588, 'Anil K', 27),
(94588, 'John V', NULL),
(94511, 'David K', 42),
(94511, 'Aryan B.', 18),
(94511, 'Lalit B.', NULL);
-- Use `REPARTITION` hint to partition the data by `zip_code` to
-- examine the `SORT BY` behavior. This is used in rest of the
-- examples.
-- Sort rows by `name` within each partition in ascending manner
SELECT /*+ REPARTITION(zip_code) */ name, age, zip_code FROM person SORT BY name;
+--------+----+--------+
| name| age|zip_code|
+--------+----+--------+
| Anil K| 27| 94588|
| Dan Li| 18| 94588|
| John V|null| 94588|
| Zen Hui| 50| 94588|
|Aryan B.| 18| 94511|
| David K| 42| 94511|
|Lalit B.|null| 94511|
+--------+----+--------+
-- Sort rows within each partition using column position.
SELECT /*+ REPARTITION(zip_code) */ name, age, zip_code FROM person SORT BY 1;
+--------+----+--------+
| name| age|zip_code|
+--------+----+--------+
| Anil K| 27| 94588|
| Dan Li| 18| 94588|
| John V|null| 94588|
| Zen Hui| 50| 94588|
|Aryan B.| 18| 94511|
| David K| 42| 94511|
|Lalit B.|null| 94511|
+--------+----+--------+
-- Sort rows within partition in ascending manner keeping null values to be last.
SELECT /*+ REPARTITION(zip_code) */ age, name, zip_code FROM person SORT BY age NULLS LAST;
+----+--------+--------+
| age| name|zip_code|
+----+--------+--------+
| 18| Dan Li| 94588|
| 27| Anil K| 94588|
| 50| Zen Hui| 94588|
|null| John V| 94588|
| 18|Aryan B.| 94511|
| 42| David K| 94511|
|null|Lalit B.| 94511|
+----+--------+--------+
-- Sort rows by age within each partition in descending manner, which defaults to NULL LAST.
SELECT /*+ REPARTITION(zip_code) */ age, name, zip_code FROM person SORT BY age DESC;
+----+--------+--------+
| age| name|zip_code|
+----+--------+--------+
| 50| Zen Hui| 94588|
| 27| Anil K| 94588|
| 18| Dan Li| 94588|
|null| John V| 94588|
| 42| David K| 94511|
| 18|Aryan B.| 94511|
|null|Lalit B.| 94511|
+----+--------+--------+
-- Sort rows by age within each partition in descending manner keeping null values to be first.
SELECT /*+ REPARTITION(zip_code) */ age, name, zip_code FROM person SORT BY age DESC NULLS FIRST;
+----+--------+--------+
| age| name|zip_code|
+----+--------+--------+
|null| John V| 94588|
| 50| Zen Hui| 94588|
| 27| Anil K| 94588|
| 18| Dan Li| 94588|
|null|Lalit B.| 94511|
| 42| David K| 94511|
| 18|Aryan B.| 94511|
+----+--------+--------+
-- Sort rows within each partition based on more than one column with each column having
-- different sort direction.
SELECT /*+ REPARTITION(zip_code) */ name, age, zip_code FROM person
SORT BY name ASC, age DESC;
+--------+----+--------+
| name| age|zip_code|
+--------+----+--------+
| Anil K| 27| 94588|
| Dan Li| 18| 94588|
| John V|null| 94588|
| Zen Hui| 50| 94588|
|Aryan B.| 18| 94511|
| David K| 42| 94511|
|Lalit B.|null| 94511|
+--------+----+--------+
{% endhighlight %}
### Related Statements
* [SELECT Main](sql-ref-syntax-qry-select.html)
* [WHERE Clause](sql-ref-syntax-qry-select-where.html)
* [GROUP BY Clause](sql-ref-syntax-qry-select-groupby.html)
* [HAVING Clause](sql-ref-syntax-qry-select-having.html)
* [ORDER BY Clause](sql-ref-syntax-qry-select-orderby.html)
* [CLUSTER BY Clause](sql-ref-syntax-qry-select-clusterby.html)
* [DISTRIBUTE BY Clause](sql-ref-syntax-qry-select-distribute-by.html)
* [LIMIT Clause](sql-ref-syntax-qry-select-limit.html)
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