COLLECT_LIST

COLLECT_LIST

description

Syntax

ARRAY<T> collect_list(expr[,max_size])

返回一个包含 expr 中所有元素(不包括NULL)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_array。

example

mysql> select k1,k2,k3 from collect_list_test order by k1;
+------+------------+-------+
| k1   | k2         | k3    |
+------+------------+-------+
|    1 | 2023-01-01 | hello |
|    2 | 2023-01-02 | NULL  |
|    2 | 2023-01-02 | hello |
|    3 | NULL       | world |
|    3 | 2023-01-02 | hello |
|    4 | 2023-01-02 | sql   |
|    4 | 2023-01-03 | sql   |
+------+------------+-------+

mysql> select collect_list(k1),collect_list(k1,3) from collect_list_test;
+-------------------------+--------------------------+
| collect_list(`k1`)      | collect_list(`k1`,3)     |
+-------------------------+--------------------------+
| [1,2,2,3,3,4,4]         | [1,2,2]                  |
+-------------------------+--------------------------+

mysql> select k1,collect_list(k2),collect_list(k3,1) from collect_list_test group by k1 order by k1;
+------+-------------------------+--------------------------+
| k1   | collect_list(`k2`)      | collect_list(`k3`,1)     |
+------+-------------------------+--------------------------+
|    1 | [2023-01-01]            | [hello]                  |
|    2 | [2023-01-02,2023-01-02] | [hello]                  |
|    3 | [2023-01-02]            | [world]                  |
|    4 | [2023-01-02,2023-01-03] | [sql]                    |
+------+-------------------------+--------------------------+

keywords

COLLECT_LIST,GROUP_ARRAY,COLLECT_SET,ARRAY