Question

I’m trying to select some information using SQL, but with no success. Here’s what I’m trying to do.

I have 2 tables:

Table employees with following columns:

IDemployee | name    | surname  | department_id
1          | John    | Smith    | 1
2          | Jane    | Smith    | 1
3          | Neo     | Anderson | 1
4          | John    | Mason    | 2
5          | James   | Cameron  | 2
6          | Morpheus| Grumpy   | 2

Table departments with columns:

IDdepartment | name
1            | Thieves
2            | Madmen

I want to select surnames of first and last employees of every department and count of their employees.
Result:

department_name | first_employee | last_employee | employee_count
Thieves         | Smith          | Anderson      | 3
Madmen          | Mason          | Grumpy        | 3

I was able to get count and ID’s of first and last employees with following query:

SELECT d.IDdepartment, COUNT(*) as "employee_count", MIN(e.IDemployee) as "first_employee", MAX(e.IDemployee) as "last_employee"
        FROM ( employees e INNER JOIN departments d ON d.IDdepartment=e.department_id)
        GROUP BY d.name;

However, I can’t find the right way to select their surnames. Any help would be greatly appreciated.

Answer 1

While there might be another way, one way is to use your query as a subquery:

SELECT d.name department_name, 
  e.surname first_employee,
  e2.surname last_employee,
  t.employee_count
FROM (
    SELECT d.IDdepartment, 
       COUNT(*) as "employee_count", 
       MIN(e.IDemployee) as "first_employee", 
       MAX(e.IDemployee) as "last_employee"
    FROM employees e 
          INNER JOIN departments d 
            ON d.IDdepartment=e.department_id
    GROUP BY d.name
  ) t JOIN employees e on t.first_employee = e.IDemployee
  JOIN employees e2 on t.last_employee = e2.IDemployee
  JOIN departments d on t.IDdepartment = d.IDdepartment

And here is the fiddle: http://sqlfiddle.com/#!2/17a5b/2

Good luck.