any_value

功能

在包含 GROUP BY 的聚合查询中，该函数用于从每个聚合分组中随机选择一行返回。

语法

ANY_VALUE(expr)

参数说明

expr: 选取的表达式。从 3.2 版本起，expr 支持 ARRAY/MAP/STRUCT 类型。

返回值说明

在每个聚合后的分组中随机选择某行的结果返回，结果是不确定的。

示例

假设有如下表。

CREATE TABLE t0(
  a INT,
  b BIGINT,
  c SMALLINT,
  d ARRAY<INT>,
  e JSON,
  f MAP<INT, INT>,
  g STRUCT<a STRING, b INT>
)
DUPLICATE KEY(a)
DISTRIBUTED BY HASH(a);

INSERT INTO t0 VALUES
(1, 1, 1, [2,3,4],parse_json('{"a":1, "b":true}'), map{1:1,3:4}, row(1, 2)),
(1, 2, 1, [2,3,5],parse_json('{"a":2, "b":true}'), map{1:2,3:3},row(2, 2)),
(2, 1, 1, [2,3,6],parse_json('{"a":3, "b":true}'), map{2:1,3:2},row(3, 2)),
(2, 2, 2, [2,4,5],parse_json('{"a":4, "b":false}'),map{1:3,3:1},row(4, 2)),
(3, 1, 1, [3,3,5],parse_json('{"a":5, "b":false}'),map{2:1,3:3},row(1, 2));

mysql> select * from t0 order by a;
+------+------+------+---------+----------------------+-----------+-----------------+
| a    | b    | c    | d       | e                    | f         | g               |
+------+------+------+---------+----------------------+-----------+-----------------+
|    1 |    1 |    1 | [2,3,4] | {"a": 1, "b": true}  | {1:1,3:4} | {"a":"1","b":2} |
|    1 |    2 |    1 | [2,3,5] | {"a": 2, "b": true}  | {1:2,3:3} | {"a":"2","b":2} |
|    2 |    1 |    1 | [2,3,6] | {"a": 3, "b": true}  | {2:1,3:2} | {"a":"3","b":2} |
|    2 |    2 |    2 | [2,4,5] | {"a": 4, "b": false} | {1:3,3:1} | {"a":"4","b":2} |
|    3 |    1 |    1 | [3,3,5] | {"a": 5, "b": false} | {2:1,3:3} | {"a":"1","b":2} |
+------+------+------+---------+----------------------+-----------+-----------------+
5 rows in set (0.01 sec)

使用 ANY_VALUE 后的结果。可以看到对于 a=1 和 a=2，随机返回了一条 b 记录。

mysql> select a,any_value(b),sum(c) from t0 group by a;
+------+----------------+----------+
| a    | any_value(`b`) | sum(`c`) |
+------+----------------+----------+
|    1 |              1 |        2 |
|    2 |              1 |        3 |
|    3 |              1 |        1 |
+------+----------------+----------+
3 rows in set (0.01 sec)

mysql> select a,any_value(d),sum(b) from t0 group by a;
+------+--------------+--------+
| a    | any_value(d) | sum(b) |
+------+--------------+--------+
|    3 | [3,3,5]      |      1 |
|    1 | [2,3,4]      |      3 |
|    2 | [2,3,6]      |      3 |
+------+--------------+--------+
2 rows in set (0.01 sec)