Select users belonging only to particular departments

Question

I have the following table with two fields namely a and b as shown below:

create table employe
(
    empID varchar(10),
    department varchar(10)
);
         


        

Answer 1

Solution using where clause:

select distinct e.empID
from employe e
where exists( select * 
              from employe
              where empID = e.empID
              having count(department) = count(case when department in('Y','X','Z') then department end)
                 and count(distinct department) = 3)

exists checks if there are records for specific EmpId that have total count of departments equal to conditional count of only matching departments and that it is also equal to the number of departments provided to the in clause. Also worth mentioning that here we apply having clause without the group by clause, on the whole set, but with already specified, only one empID.

SQLFiddle

You can achieve this without the correlated subquery, but with the group by clause:

select e.empId
from employe e
group by e.empID
having count(department) = count(case when department in('Y','X','Z') then department end)
   and count(distinct department) = 3

SQLFiddle

You can also use another variation of having clause for the query above:

having count(case when department not in('Y','X', 'Z') then department end) = 0
   and count(distinct case when department in('Y','X','Z') then department end) = 3

SQLFiddle