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### What changes were proposed in this pull request? A few improvements to the sql ref SELECT doc: 1. correct the syntax of SELECT query 2. correct the default of null sort order 3. correct the GROUP BY syntax 4. several minor fixes ### Why are the changes needed? refine document ### Does this PR introduce any user-facing change? N/A ### How was this patch tested? N/A Closes #27866 from cloud-fan/doc. Authored-by: Wenchen Fan <wenchen@databricks.com> Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>
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| 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. |
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 %}