Postgres 13

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create table users (id int primary key);
create table events (id int primary key, title varchar(255), content varchar(255), status int, creator int references users);
create table accounts (user_id int references users, name varchar(255), surname varchar(255));
create table events_user (id int primary key, events_id int references events, users_id int references users);

insert into users values (1), (2), (3);
insert into accounts values (1, 'Name1', 'Surname1');
insert into accounts values (2, 'Name2', 'Surname2');
insert into events values (1, 'fffffff', 'bla', 1, 1);
insert into events values (2, 'event 2', 'blabla', 42, 1);
--insert into events_user values (1, 1, 1);
--insert into events_user values (2, 1, 2);
--insert into events_user values (3, 2, 2);

SELECT
    events.id, events.title, events.creator, events.content, events.status,
    (json_agg(json_build_object('name', a.name, 'surname', a.surname)) -> 0) AS creator,
    case when count(t1.user_id) = 0 then '[]' else json_agg(json_build_object('id', t1.user_id, 'name', t1.name, 'surname', t1.surname)) end  members
FROM
    events
INNER JOIN 	
    accounts a ON  events.creator=a.user_id
LEFT JOIN (
  SELECT events_id AS id, 
          a.user_id,
          a.name,
          a.surname
  FROM events_user e
  INNER JOIN accounts a ON a.user_id = e.users_id
) t1 ON t1.id = events.id
WHERE events.id = 1 
GROUP BY events.id, events.title, events.creator, events.content, events.status

3 rows affected

1 rows affected

1 rows affected

1 rows affected

1 rows affected

id	title	creator	content	status	creator	members
1	fffffff	1	bla	1	{"name" : "Name1", "surname" : "Surname1"}	[]