MAP_AGG
更新时间:2025-10-16
描述
MAP_AGG 函数用于根据多行数据中的键值对形成一个映射结构。
语法
MAP_AGG(<expr1>, <expr2>)
参数说明
参数 | 说明 |
---|---|
<expr1> |
用于指定作为键的表达式。 |
<expr2> |
用于指定作为对应的值的表达式。 |
返回值
返回映射后的 MAP 类型的值。
举例
SQL
1select `n_nationkey`, `n_name`, `n_regionkey` from `nation`;
Text
1+-------------+----------------+-------------+
2| n_nationkey | n_name | n_regionkey |
3+-------------+----------------+-------------+
4| 0 | ALGERIA | 0 |
5| 1 | ARGENTINA | 1 |
6| 2 | BRAZIL | 1 |
7| 3 | CANADA | 1 |
8| 4 | EGYPT | 4 |
9| 5 | ETHIOPIA | 0 |
10| 6 | FRANCE | 3 |
11| 7 | GERMANY | 3 |
12| 8 | INDIA | 2 |
13| 9 | INDONESIA | 2 |
14| 10 | IRAN | 4 |
15| 11 | IRAQ | 4 |
16| 12 | JAPAN | 2 |
17| 13 | JORDAN | 4 |
18| 14 | KENYA | 0 |
19| 15 | MOROCCO | 0 |
20| 16 | MOZAMBIQUE | 0 |
21| 17 | PERU | 1 |
22| 18 | CHINA | 2 |
23| 19 | ROMANIA | 3 |
24| 20 | SAUDI ARABIA | 4 |
25| 21 | VIETNAM | 2 |
26| 22 | RUSSIA | 3 |
27| 23 | UNITED KINGDOM | 3 |
28| 24 | UNITED STATES | 1 |
29+-------------+----------------+-------------+
SQL
1select `n_regionkey`, map_agg(`n_nationkey`, `n_name`) from `nation` group by `n_regionkey`;
Text
1+-------------+---------------------------------------------------------------------------+
2| n_regionkey | map_agg(`n_nationkey`, `n_name`) |
3+-------------+---------------------------------------------------------------------------+
4| 1 | {1:"ARGENTINA", 2:"BRAZIL", 3:"CANADA", 17:"PERU", 24:"UNITED STATES"} |
5| 0 | {0:"ALGERIA", 5:"ETHIOPIA", 14:"KENYA", 15:"MOROCCO", 16:"MOZAMBIQUE"} |
6| 3 | {6:"FRANCE", 7:"GERMANY", 19:"ROMANIA", 22:"RUSSIA", 23:"UNITED KINGDOM"} |
7| 4 | {4:"EGYPT", 10:"IRAN", 11:"IRAQ", 13:"JORDAN", 20:"SAUDI ARABIA"} |
8| 2 | {8:"INDIA", 9:"INDONESIA", 12:"JAPAN", 18:"CHINA", 21:"VIETNAM"} |
9+-------------+---------------------------------------------------------------------------+
SQL
1select n_regionkey, map_agg(`n_name`, `n_nationkey` % 5) from `nation` group by `n_regionkey`;
Text
1+-------------+------------------------------------------------------------------------+
2| n_regionkey | map_agg(`n_name`, (`n_nationkey` % 5)) |
3+-------------+------------------------------------------------------------------------+
4| 2 | {"INDIA":3, "INDONESIA":4, "JAPAN":2, "CHINA":3, "VIETNAM":1} |
5| 0 | {"ALGERIA":0, "ETHIOPIA":0, "KENYA":4, "MOROCCO":0, "MOZAMBIQUE":1} |
6| 3 | {"FRANCE":1, "GERMANY":2, "ROMANIA":4, "RUSSIA":2, "UNITED KINGDOM":3} |
7| 1 | {"ARGENTINA":1, "BRAZIL":2, "CANADA":3, "PERU":2, "UNITED STATES":4} |
8| 4 | {"EGYPT":4, "IRAN":0, "IRAQ":1, "JORDAN":3, "SAUDI ARABIA":0} |
9+-------------+------------------------------------------------------------------------+