COLLECT_LIST

Description

Aggregation function, used to aggregate all values of a column into an array.

Alias

• GROUP_ARRAY

Syntax

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

Parameters

Parameter	Description
<expr>	Column or expression to aggregate
<max_size>	Optional parameter that can be set to limit the size of the resulting array to max_size elements

Return Value

The return type is ARRAY, which contains all values. Special circumstances:

• If the value is NULL, it will filter

Example

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   |
+------+------------+-------+

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]                  |
+-------------------------+--------------------------+

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]                    |
+------+-------------------------+--------------------------+