json - postgresql 中分组依据的嵌套 json 聚合行

Question

我有一个postgresql表

alok=# select * from people;
  name   | country |  city   
---------+---------+---------
 alok    | india   | delhi
 ram     | india   | kolkata
 shyam   | india   | kanpur
 krishna | us      | newyork
 ajit    | india   | delhi
 sami    | india   | delhi
 mohamad | india   | kolkata
(7 rows)

可以生成

create table people(name varchar, country varchar, city varchar);

insert into people values('alok', 'india', 'delhi');
insert into people values('ram', 'india', 'kolkata');
insert into people values('shyam', 'india', 'kanpur');
insert into people values('krishna', 'us', 'newyork');
insert into people values('ajit', 'india', 'delhi');
insert into people values('sami', 'india', 'delhi');
insert into people values('mohamad', 'india', 'kolkata');

我想生成国家和城市的聚合名称，例如

country |                name                
---------+------------------------------------
 india   | {"delhi":["alok", "ajit", "sami"], "kolkata":["ram", "mohamad"], "kanpur":["shyam"]}
 us      | {"newyork":["krishna"]}

Answer 1

demo:db<>fiddle

SELECT 
    country,
    json_object_agg(city, agg_names)
FROM (
    SELECT
        country,
        city, 
        json_agg(name) AS agg_names
    FROM
        people
    GROUP BY country, city
) s
GROUP BY country

1. 按城市 对名称进行分组。要将 name 放入一个 JSON 数组中，您可以使用聚合函数 json_agg()
2. 按国家/地区 将此结果分组。要获得预期的输出，您需要使用聚合函数 json_object_agg()，它从 city 和 name 数组

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