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>
110 lines
3.2 KiB
Markdown
110 lines
3.2 KiB
Markdown
---
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layout: global
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title: LIMIT Clause
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displayTitle: LIMIT Clause
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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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The <code>LIMIT</code> clause is used to constrain the number of rows returned by
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the [SELECT](sql-ref-syntax-qry-select.html) statement. In general, this clause
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is used in conjunction with [ORDER BY](sql-ref-syntax-qry-select-orderby.html) to
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ensure that the results are deterministic.
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### Syntax
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{% highlight sql %}
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LIMIT { ALL | integer_expression }
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{% endhighlight %}
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### Parameters
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<dl>
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<dt><code><em>ALL</em></code></dt>
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<dd>
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If specified, the query returns all the rows. In other words, no limit is applied if this
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option is specified.
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</dd>
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<dt><code><em>integer_expression</em></code></dt>
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<dd>
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Specifies a foldable expression that returns an integer.
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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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CREATE TABLE person (name STRING, age INT);
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INSERT INTO person VALUES
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('Zen Hui', 25),
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('Anil B', 18),
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('Shone S', 16),
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('Mike A', 25),
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('John A', 18),
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('Jack N', 16);
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-- Select the first two rows.
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SELECT name, age FROM person ORDER BY name LIMIT 2;
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+------+---+
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| name|age|
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+------+---+
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|Anil B| 18|
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|Jack N| 16|
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+------+---+
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-- Specifying ALL option on LIMIT returns all the rows.
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SELECT name, age FROM person ORDER BY name LIMIT ALL;
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+-------+---+
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| name|age|
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+-------+---+
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| Anil B| 18|
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| Jack N| 16|
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| John A| 18|
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| Mike A| 25|
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|Shone S| 16|
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|Zen Hui| 25|
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+-------+---+
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-- A function expression as an input to LIMIT.
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SELECT name, age FROM person ORDER BY name LIMIT length('SPARK');
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+-------+---+
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| name|age|
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+-------+---+
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| Anil B| 18|
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| Jack N| 16|
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| John A| 18|
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| Mike A| 25|
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|Shone S| 16|
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+-------+---+
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-- A non-foldable expression as an input to LIMIT is not allowed.
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SELECT name, age FROM person ORDER BY name LIMIT length(name);
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org.apache.spark.sql.AnalysisException: The limit expression must evaluate to a constant value ...
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{% endhighlight %}
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### Related Statements
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* [SELECT Main](sql-ref-syntax-qry-select.html)
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* [WHERE Clause](sql-ref-syntax-qry-select-where.html)
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* [GROUP BY Clause](sql-ref-syntax-qry-select-groupby.html)
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* [HAVING Clause](sql-ref-syntax-qry-select-having.html)
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* [ORDER BY Clause](sql-ref-syntax-qry-select-orderby.html)
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* [SORT BY Clause](sql-ref-syntax-qry-select-sortby.html)
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* [CLUSTER BY Clause](sql-ref-syntax-qry-select-clusterby.html)
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* [DISTRIBUTE BY Clause](sql-ref-syntax-qry-select-distribute-by.html)
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