COLLECT_SET

Description

Aggregation function aggregates all unique values of the specified column, removes duplicate elements, and returns a set type result.

Alias

GROUP_UNIQ_ARRAY

Syntax

COLLECT_SET(<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. This array contains all values after deduplication. Special case:

If the value is NULL, it will filter

Example

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

COLLECT_LIST CORR