LIMIT 子句LIMIT clause

限制 SELECT 語句所傳回的資料列數目。Constrains the number of rows returned by the SELECT statement. 一般來說,這個子句會與 ORDER BY 搭配使用,以確保結果具有決定性。In general, this clause is used in conjunction with ORDER BY to ensure that the results are deterministic.

語法Syntax

LIMIT { ALL | integer_expression }

參數Parameters

  • ALLALL

    如果有指定,查詢會傳回所有資料列。If specified, the query returns all the rows. 換句話說,如果指定此選項,則不會套用任何限制。In other words, no limit is applied if this option is specified.

  • integer_expressioninteger_expression

    可折迭的運算式,會傳回整數。A foldable expression that returns an integer.

範例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 ...