SQL count by n-tuples
You can use LISTAGG() function to gather the groups/tuples, then another GROUP BY to count occurrences of every group/tuple.  

Assuming that (order_number, value) is unique, i.e. that no two rows have the same order_number and value:

WITH groups AS
  ( SELECT LISTAGG(value, '-') WITHIN GROUP (ORDER BY value) AS value_group
    FROM employees
    GROUP BY order_number
  )
SELECT value_group,
       COUNT(*) AS occurrences
FROM groups
GROUP BY value_group ;


You could also get the order numbers that belong to each group:

WITH groups AS
  ( SELECT LISTAGG(value, '-') WITHIN GROUP (ORDER BY value) 
             AS value_group,
           order_number
    FROM employees
    GROUP BY order_number
  )
SELECT value_group,
       COUNT(*) AS occurrences,
       LISTAGG(order_number, ', ') WITHIN GROUP (ORDER BY order_number) 
         AS order_numbers
FROM groups
GROUP BY value_group ;