LATERAL VIEW 子句

与生成器函数(例如 EXPLODE)结合使用,将生成包含一个或多个行的虚拟表。 LATERAL VIEW 将行应用于每个原始输出行。

语法

LATERAL VIEW [ OUTER ] generator_function ( expression [ , ... ] ) [ table_alias ] AS column_alias [ , ... ]

参数

  • OUTER

    如果指定了 OUTER,则输入数组/映射为空或为 Null 时返回 Null。

  • generator_function

    生成器函数(EXPLODE、INLINE 等)。

  • table_alias

    generator_function 的别名,它是可选项。

  • column_alias

    列出列别名 generator_function,它可用于输出行。 如果 generator_function 有多个输出列,则可能有多个别名。

示例

CREATE TABLE person (id INT, name STRING, age INT, class INT, address STRING);
INSERT INTO person VALUES
    (100, 'John', 30, 1, 'Street 1'),
    (200, 'Mary', NULL, 1, 'Street 2'),
    (300, 'Mike', 80, 3, 'Street 3'),
    (400, 'Dan', 50, 4, 'Street 4');

SELECT * FROM person
    LATERAL VIEW EXPLODE(ARRAY(30, 60)) tabelName AS c_age
    LATERAL VIEW EXPLODE(ARRAY(40, 80)) AS d_age;
+------+-------+-------+--------+-----------+--------+--------+
|  id  | name  |  age  | class  |  address  | c_age  | d_age  |
+------+-------+-------+--------+-----------+--------+--------+
| 100  | John  | 30    | 1      | Street 1  | 30     | 40     |
| 100  | John  | 30    | 1      | Street 1  | 30     | 80     |
| 100  | John  | 30    | 1      | Street 1  | 60     | 40     |
| 100  | John  | 30    | 1      | Street 1  | 60     | 80     |
| 200  | Mary  | NULL  | 1      | Street 2  | 30     | 40     |
| 200  | Mary  | NULL  | 1      | Street 2  | 30     | 80     |
| 200  | Mary  | NULL  | 1      | Street 2  | 60     | 40     |
| 200  | Mary  | NULL  | 1      | Street 2  | 60     | 80     |
| 300  | Mike  | 80    | 3      | Street 3  | 30     | 40     |
| 300  | Mike  | 80    | 3      | Street 3  | 30     | 80     |
| 300  | Mike  | 80    | 3      | Street 3  | 60     | 40     |
| 300  | Mike  | 80    | 3      | Street 3  | 60     | 80     |
| 400  | Dan   | 50    | 4      | Street 4  | 30     | 40     |
| 400  | Dan   | 50    | 4      | Street 4  | 30     | 80     |
| 400  | Dan   | 50    | 4      | Street 4  | 60     | 40     |
| 400  | Dan   | 50    | 4      | Street 4  | 60     | 80     |
+------+-------+-------+--------+-----------+--------+--------+

SELECT c_age, COUNT(1) FROM person
    LATERAL VIEW EXPLODE(ARRAY(30, 60)) AS c_age
    LATERAL VIEW EXPLODE(ARRAY(40, 80)) AS d_age
GROUP BY c_age;
+--------+-----------+
| c_age  | count(1)  |
+--------+-----------+
| 60     | 8         |
| 30     | 8         |
+--------+-----------+

SELECT * FROM person
    LATERAL VIEW EXPLODE(ARRAY()) tabelName AS c_age;
+-----+-------+------+--------+----------+--------+
| id  | name  | age  | class  | address  | c_age  |
+-----+-------+------+--------+----------+--------+
+-----+-------+------+--------+----------+--------+

SELECT * FROM person
    LATERAL VIEW OUTER EXPLODE(ARRAY()) tabelName AS c_age;
+------+-------+-------+--------+-----------+--------+
|  id  | name  |  age  | class  |  address  | c_age  |
+------+-------+-------+--------+-----------+--------+
| 100  | John  | 30    | 1      | Street 1  | NULL   |
| 200  | Mary  | NULL  | 1      | Street 2  | NULL   |
| 300  | Mike  | 80    | 3      | Street 3  | NULL   |
| 400  | Dan   | 50    | 4      | Street 4  | NULL   |
+------+-------+-------+--------+-----------+--------+