LIMIT 子句
描述
LIMIT 子句用于限制 SELECT 语句返回的行数。通常，此子句与 ORDER BY 结合使用，以确保结果具有确定性。
语法
LIMIT { ALL | integer_expression }
参数
-
ALL
如果指定，查询将返回所有行。换句话说，如果指定此选项，则不应用任何限制。
-
integer_expression
指定一个可折叠的表达式，该表达式返回一个整数。
示例
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 ...