SQL select groups where values are exclusively in a list - sql

Question

Given a table with two columns, department and employee, where every employee belongs to 1 department.
Given a list of employee ids, how do I select departments where all employees are in the list?
Department
Employee
finance
1
finance
2
marketing
3
marketing
4
IT
5
IT
6
given (2,3,4,5,6), returns ('marketing', 'IT')
(Note: DB flavor does not matter to me, you may use standard or DB-specific SQL)

Answer 1

Put your input id's into a table, join to the existing table, and check counts between input and the existing employees. If they match, output.
Change this to whatever RDBMS you're using
CREATE TEMP TABLE input_vals (id int);
insert into input_vals
values
(2),
(3),
(4),
(5),
(6);
with cte_joins AS (
select ot.department,
count(ot.employee) AS employee_count1,
sum(case when iv.id is not null then 1 else 0 end) AS employee_count2
from orig_table ot
left join input_vals iv
on ot.employee = iv.id
group by ot.department
)
select department
from cte_joins
where employee_count1 = employee_count2

Answer 2

You can use a couple of derived tables - one to get the count of employees in each department and one to get the count of employees in each department limited by your list of employees. Return the ones that match.
select
distinct full_list.department
from (
select
department,
count (*) as cnt
from
<your table>
group by department) full_list
inner join (
select
department,
count (*) as cnt
from
<your table>
group by department
where
employee in (2,3,4,5,6)
) limited_list
on full_list.department = limited_list.department
and full_list.cnt = limited_list.cnt

Answer 3

-- departments
select department from t where employee in (2,3,4,5,6);
-- departments containing extra persons
select department from t
where department in (select department from t where employee in (2,3,4,5,6))
and employee not in (2,3,4,5,6);
--- departments, employees from the list, with no extra
select department from t
where employee in (2,3,4,5,6) and department not in (
select department from t
where department in (
select department from t where employee in (2,3,4,5,6)
) and employee not in (2,3,4,5,6)
)

Answer 4

Assume you employee list is captured as a column in a table. Since you didn't provide any detail on the tool set you are using.
Something like this is a common pattern, depending on your dbms there's other more simple syntax.
select distinct
de.department
from department_employee de
where not exists
( select 1
from department_employee de2
where not exists
( select 1
from employee_list el
where de2.employee = el.employee
)
and de.department = de2.department
);