Json in Postgresql - json

Question

I'm learning Postgresql and Json.
I have for example database like that:
CREATE TABLE employees (
employee_id serial primary key,
department_id integer references departments(department_id),
name text,
start_date date,
fingers integer,
geom geometry(point, 4326)
);
CREATE TABLE departments (
department_id bigint primary key,
name text
);
INSERT INTO departments
(department_id, name)
VALUES
(1, 'spatial'),
(2, 'cloud');
INSERT INTO employees
(department_id, name, start_date, fingers, geom)
VALUES
(1, 'Paul', '2018/09/02', 10, 'POINT(-123.32977 48.40732)'),
(1, 'Martin', '2019/09/02', 9, 'POINT(-123.32977 48.40732)'),
(2, 'Craig', '2019/11/01', 10, 'POINT(-122.33207 47.60621)'),
(2, 'Dan', '2020/10/01', 8, 'POINT(-122.33207 47.60621)');
How could i do so i could get the data like this:
[
{
"department_name": "cloud",
"employees": [
{
"name": "Craig",
"start_date": "2019-11-01"
},
{
"name": "Dan",
"start_date": "2020-10-01"
}
]
},
{
"department_name": "spatial",
"employees": [
{
"name": "Paul",
"start_date": "2018-09-02"
},
{
"name": "Martin",
"start_date": "2019-09-02"
}
]
}
]

Answer 1

follow this link: https://dba.stackexchange.com/questions/69655/select-columns-inside-json-agg/200240#200240
CREATE TEMP TABLE x (
name text,
start_date date
);
WITH cte AS (
SELECT
d.name AS department_name,
json_agg((e.name, e.start_date)::x) AS employees
FROM
departments d
JOIN employees e ON d.department_id = e.department_id
GROUP BY
1
)
SELECT
json_agg((row_to_json(cte.*)))
FROM
cte;