The MAP_AGG function is used to form a mapping structure based on key-value pairs from multiple rows of data.
MAP_AGG(<expr1>, <expr2>)
| Parameters | Description |
|---|---|
<expr1> | The expression used to specify the key. |
<expr2> | The expression used to specify the corresponding value. |
Returns a value of the MAP type.
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 | +-------------+----------------+-------------+
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"} | +-------------+---------------------------------------------------------------------------+
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} | +-------------+------------------------------------------------------------------------+