COLLECT_SET
COLLECT_SET
COLLECT_SET
description
Syntax
ARRAY<T> collect_set(expr[,max_size])
返回一个对expr去重后的数组。可选参数max_size，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。
得到的结果数组中不包含NULL元素，数组中的元素顺序不固定。该函数具有别名group_uniq_array。
notice
仅支持向量化引擎中使用
example
mysql> set enable_vectorized_engine=true;
mysql> 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 |
+------+------------+-------+
mysql> 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] |
+----------------------------------------------------+
mysql> 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] |
+------+-------------------------+--------------------------+
keywords
COLLECT_SET,GROUP_UNIQ_ARRAY,COLLECT_LIST,ARRAY
