MySQL 8.0

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select version();


version()


8.0.22


create table user (id_user int, first_name varchar (30), last_name varchar (30))
create table employee (id_employee int, user_id int, team_id int)
create table team(id_team int,name varchar (30))
create table team_object(id_team_object int, id_team int, id_object int)
with q as (
  select
  employee.user_id, count(team_object.id_team_object) as count
  from team_object
  join employee on employee.team_id = team_object.id_team
  group by employee.user_id
)
select first_name, last_name
from user
join q on q.user_id = user.id_user and q.count = (select max(count) from q)