Get RID of DISTINCT in SELECT

Question

Hi,

 

I have a SQL query that looks like this:

 

SELECT department, count(distinct person_id) AS NumberOfPersons
FROM    person
GROUP BY department

 

This query wil show me how many persons that are employed on departments. A person with same person_id can exist on several records in the person table therefore I have used distinct before count.

 

Because of performance issue I did not want to use DISTINCT!

 

How can I rewrite this SQL whith no DISTINCT in the SELECT statement?