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>
3.2 KiB
| layout | title | displayTitle | license |
|---|---|---|---|
| global | LIMIT Clause | LIMIT Clause | 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 LIMIT clause is used to constrain the number of rows returned by
the SELECT statement. In general, this clause
is used in conjunction with ORDER BY to
ensure that the results are deterministic.
Syntax
{% highlight sql %} LIMIT { ALL | integer_expression } {% endhighlight %}
Parameters
ALL- If specified, the query returns all the rows. In other words, no limit is applied if this option is specified.
integer_expression- Specifies a foldable expression that returns an integer.
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);
-- Select the first two rows. SELECT name, age FROM person ORDER BY name LIMIT 2; +------+---+ | name|age| +------+---+ |Anil B| 18| |Jack N| 16| +------+---+
-- Specifying ALL option on LIMIT returns all the rows. SELECT name, age FROM person ORDER BY name LIMIT ALL; +-------+---+ | name|age| +-------+---+ | Anil B| 18| | Jack N| 16| | John A| 18| | Mike A| 25| |Shone S| 16| |Zen Hui| 25| +-------+---+
-- A function expression as an input to LIMIT. SELECT name, age FROM person ORDER BY name LIMIT length('SPARK'); +-------+---+ | name|age| +-------+---+ | Anil B| 18| | Jack N| 16| | John A| 18| | Mike A| 25| |Shone S| 16| +-------+---+
-- A non-foldable expression as an input to LIMIT is not allowed. SELECT name, age FROM person ORDER BY name LIMIT length(name); org.apache.spark.sql.AnalysisException: The limit expression must evaluate to a constant value ... {% endhighlight %}