LIMIT 子句 (SQL Analytics)LIMIT clause (SQL Analytics)

限制 SELECT 语句返回的行数。Constrains the number of rows returned by the SELECT statement. 通常,此子句会与 ORDER BY 结合使用,以确保结果是确定的。In general, this clause is used in conjunction with ORDER BY to ensure that the results are deterministic.

语法Syntax

LIMIT { ALL | integer_expression }

参数Parameters

  • ALLALL

    如果指定了它,查询将返回所有行。If specified, the query returns all the rows. 换句话说,如果指定了此选项,则没有限制。In other words, no limit is applied if this option is specified.

  • integer_expressioninteger_expression

    一个返回整数的可折叠表达式。A foldable expression that returns an integer.

示例Examples

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 ...