MAP_AGG
description
Syntax
MAP_AGG(expr1, expr2)
返回一个 map, 由 expr1 作为键，expr2 作为对应的值。
example
MySQL > select `n_nationkey`, `n_name`, `n_regionkey` from `nation`;
+-------------+----------------+-------------+
| n_nationkey | n_name | n_regionkey |
+-------------+----------------+-------------+
| 0 | ALGERIA | 0 |
| 1 | ARGENTINA | 1 |
| 2 | BRAZIL | 1 |
| 3 | CANADA | 1 |
| 4 | EGYPT | 4 |
| 5 | ETHIOPIA | 0 |
| 6 | FRANCE | 3 |
| 7 | GERMANY | 3 |
| 8 | INDIA | 2 |
| 9 | INDONESIA | 2 |
| 10 | IRAN | 4 |
| 11 | IRAQ | 4 |
| 12 | JAPAN | 2 |
| 13 | JORDAN | 4 |
| 14 | KENYA | 0 |
| 15 | MOROCCO | 0 |
| 16 | MOZAMBIQUE | 0 |
| 17 | PERU | 1 |
| 18 | CHINA | 2 |
| 19 | ROMANIA | 3 |
| 20 | SAUDI ARABIA | 4 |
| 21 | VIETNAM | 2 |
| 22 | RUSSIA | 3 |
| 23 | UNITED KINGDOM | 3 |
| 24 | UNITED STATES | 1 |
+-------------+----------------+-------------+
MySQL > select `n_regionkey`, map_agg(`n_nationkey`, `n_name`) from `nation` group by `n_regionkey`;
+-------------+---------------------------------------------------------------------------+
| n_regionkey | map_agg(`n_nationkey`, `n_name`) |
+-------------+---------------------------------------------------------------------------+
| 1 | {1:"ARGENTINA", 2:"BRAZIL", 3:"CANADA", 17:"PERU", 24:"UNITED STATES"} |
| 0 | {0:"ALGERIA", 5:"ETHIOPIA", 14:"KENYA", 15:"MOROCCO", 16:"MOZAMBIQUE"} |
| 3 | {6:"FRANCE", 7:"GERMANY", 19:"ROMANIA", 22:"RUSSIA", 23:"UNITED KINGDOM"} |
| 4 | {4:"EGYPT", 10:"IRAN", 11:"IRAQ", 13:"JORDAN", 20:"SAUDI ARABIA"} |
| 2 | {8:"INDIA", 9:"INDONESIA", 12:"JAPAN", 18:"CHINA", 21:"VIETNAM"} |
+-------------+---------------------------------------------------------------------------+
MySQL > select n_regionkey, map_agg(`n_name`, `n_nationkey` % 5) from `nation` group by `n_regionkey`;
+-------------+------------------------------------------------------------------------+
| n_regionkey | map_agg(`n_name`, (`n_nationkey` % 5)) |
+-------------+------------------------------------------------------------------------+
| 2 | {"INDIA":3, "INDONESIA":4, "JAPAN":2, "CHINA":3, "VIETNAM":1} |
| 0 | {"ALGERIA":0, "ETHIOPIA":0, "KENYA":4, "MOROCCO":0, "MOZAMBIQUE":1} |
| 3 | {"FRANCE":1, "GERMANY":2, "ROMANIA":4, "RUSSIA":2, "UNITED KINGDOM":3} |
| 1 | {"ARGENTINA":1, "BRAZIL":2, "CANADA":3, "PERU":2, "UNITED STATES":4} |
| 4 | {"EGYPT":4, "IRAN":0, "IRAQ":1, "JORDAN":3, "SAUDI ARABIA":0} |
+-------------+------------------------------------------------------------------------+keywords
MAP_AGG