179289f0bf
### 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>
118 lines
5.3 KiB
Markdown
118 lines
5.3 KiB
Markdown
---
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layout: global
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title: DESCRIBE FUNCTION
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displayTitle: DESCRIBE FUNCTION
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license: |
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Licensed to the Apache Software Foundation (ASF) under one or more
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contributor license agreements. See the NOTICE file distributed with
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this work for additional information regarding copyright ownership.
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The ASF licenses this file to You under the Apache License, Version 2.0
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(the "License"); you may not use this file except in compliance with
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the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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---
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### Description
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`DESCRIBE FUNCTION` statement returns the basic metadata information of an
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existing function. The metadata information includes the function name, implementing
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class and the usage details. If the optional `EXTENDED` option is specified, the basic
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metadata information is returned along with the extended usage information.
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### Syntax
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{% highlight sql %}
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{ DESC | DESCRIBE } FUNCTION [ EXTENDED ] function_name
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{% endhighlight %}
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### Parameters
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<dl>
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<dt><code><em>function_name</em></code></dt>
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<dd>
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Specifies a name of an existing function in the system. The function name may be
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optionally qualified with a database name. If `function_name` is qualified with
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a database then the function is resolved from the user specified database, otherwise
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it is resolved from the current database.<br><br>
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<b>Syntax:</b>
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<code>
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[ database_name. ] function_name
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</code>
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</dd>
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</dl>
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### Examples
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{% highlight sql %}
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-- Describe a builtin scalar function.
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-- Returns function name, implementing class and usage
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DESC FUNCTION abs;
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+-------------------------------------------------------------------+
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|function_desc |
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+-------------------------------------------------------------------+
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|Function: abs |
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|Class: org.apache.spark.sql.catalyst.expressions.Abs |
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|Usage: abs(expr) - Returns the absolute value of the numeric value.|
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+-------------------------------------------------------------------+
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-- Describe a builtin scalar function.
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-- Returns function name, implementing class and usage and examples.
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DESC FUNCTION EXTENDED abs;
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+-------------------------------------------------------------------+
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|function_desc |
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+-------------------------------------------------------------------+
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|Function: abs |
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|Class: org.apache.spark.sql.catalyst.expressions.Abs |
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|Usage: abs(expr) - Returns the absolute value of the numeric value.|
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|Extended Usage: |
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| Examples: |
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| > SELECT abs(-1); |
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| 1 |
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| |
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+-------------------------------------------------------------------+
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-- Describe a builtin aggregate function
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DESC FUNCTION max;
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+--------------------------------------------------------------+
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|function_desc |
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+--------------------------------------------------------------+
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|Function: max |
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|Class: org.apache.spark.sql.catalyst.expressions.aggregate.Max|
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|Usage: max(expr) - Returns the maximum value of `expr`. |
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+--------------------------------------------------------------+
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-- Describe a builtin user defined aggregate function
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-- Returns function name, implementing class and usage and examples.
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DESC FUNCTION EXTENDED explode
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+---------------------------------------------------------------+
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|function_desc |
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+---------------------------------------------------------------+
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|Function: explode |
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|Class: org.apache.spark.sql.catalyst.expressions.Explode |
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|Usage: explode(expr) - Separates the elements of array `expr` |
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| into multiple rows, or the elements of map `expr` into |
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| multiple rows and columns. Unless specified otherwise, uses |
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| the default column name `col` for elements of the array or |
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| `key` and `value` for the elements of the map. |
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|Extended Usage: |
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| Examples: |
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| > SELECT explode(array(10, 20)); |
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| 10 |
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| 20 |
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+---------------------------------------------------------------+
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{% endhighlight %}
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### Related Statements
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* [DESCRIBE DATABASE](sql-ref-syntax-aux-describe-database.html)
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* [DESCRIBE TABLE](sql-ref-syntax-aux-describe-table.html)
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* [DESCRIBE QUERY](sql-ref-syntax-aux-describe-query.html)
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