COLLECT_SET

描述

聚合函数，聚合指定列的所有唯一值，去除重复的元素，并返回一个集合类型的结果。

别名

• GROUP_UNIQ_ARRAY

语法

COLLECT_SET(<expr> [,<max_size>])

参数

参数	说明
<expr>	要聚合的列或表达式
<max_size>	可选参数，通过设置该参数能够将结果数组的大小限制为 max_size 个元素

返回值

返回类型是 ARRAY，该数组包含去重后的所有值，特殊情况：

• 如果值为NULL，则会过滤

举例

select k1,k2,k3 from collect_set_test order by k1;

+------+------------+-------+
| k1   | k2         | k3    |
+------+------------+-------+
|    1 | 2023-01-01 | hello |
|    2 | 2023-01-01 | NULL  |
|    2 | 2023-01-02 | hello |
|    3 | NULL       | world |
|    3 | 2023-01-02 | hello |
|    4 | 2023-01-02 | doris |
|    4 | 2023-01-03 | sql   |
+------+------------+-------+

select collect_set(k1),collect_set(k1,2) from collect_set_test;

+-------------------------+--------------------------+
| collect_set(`k1`)       | collect_set(`k1`,2)      |
+-------------------------+--------------------------+
| [4,3,2,1]               | [1,2]                    |
+----------------------------------------------------+

select k1,collect_set(k2),collect_set(k3,1) from collect_set_test group by k1 order by k1;

+------+-------------------------+--------------------------+
| k1   | collect_set(`k2`)       | collect_set(`k3`,1)      |
+------+-------------------------+--------------------------+
|    1 | [2023-01-01]            | [hello]                  |
|    2 | [2023-01-01,2023-01-02] | [hello]                  |
|    3 | [2023-01-02]            | [world]                  |
|    4 | [2023-01-02,2023-01-03] | [sql]                    |
+------+-------------------------+--------------------------+