Max(count(*))

Question

countries(country_name, country_id, region_id)
Employees(employee_id,first_name, last_name, email, phone_number, hire_date, job_id, salary, commission_PCT, manager_id, department_id)
departments(department_id, location_id, manager_id, department_name)
job_history(employee_id, start_date, end_date, job_id, department_id)
jobs(job_id, job_title, min_salary, max_salary)
locations(location_id, street_address, postal_code, city, state_province, country_id)
regions(region_id, region_name)
question is display all countries that are located in the region which has most countries in the countries table
select country_name
from countries
where region_id=1
--(select max(count(*)) from countries group by region_id)Instead of using 1 where where clause, i need to write a sub query to get the region 1.

Answer 1

Oficially tested ;) :
SQL> insert into countries values('France',1,1);
1 row created.
SQL> insert into countries values('Italy',2,1);
1 row created.
SQL> insert into countries values('China',3,2);
1 row created.
SQL> insert into countries values('India',4,2);
1 row created.
SQL> insert into countries values('Mongolia',5,2);
1 row created.
SQL> select  country_name,
  2          country_id,
  3          region_id
  4    from  countries
  5    where (region_id,1) in (
  6                            select  region_id,
  7                                    dense_rank() over(order by count(*) desc) rnk
  8                              from  countries
  9                              group by region_id
10                           )
11  /
COUNTRY_NAME                   COUNTRY_ID  REGION_ID
China                                   3          2
India                                   4          2
Mongolia                                5          2
SQL> SY.