Remove multiple instances of the same person, different IDs from SQL Server

I have a data set where there are individuals appearning multiple times with the same name and SSN but different personids. I want to remove those people and only keep those that appear one time.

    declare @t table(personid int, first_name varchar(50), last_name varchar(50), ssn int)
    insert into @t
    values(1, 'Roman', 'Smith', 12),
    (2, 'John', 'Thomas', 15),
    (3, 'John', 'Thomas', 15)

In this instance I only want to return Roman Smith and eliminate John Thomas altogether.

I’ve been playing around with Window Functions and I’ve only managed to get this far:

    select * from
    (
    select person_id, first_name, last_name, middle_initial, ssn,
    row_number() over(partition by ssn, first_name, last_name, middle_initial order by person_id) as 
    rn
    from t_person
    where person_id in (1, 2, 3)
    )a
    where rn = 1

Answer

In this scenario I like to use NOT EXISTS. Easy way to perform elimination.

SELECT * 
FROM @t AS T 
WHERE NOT EXISTS (SELECT 1 FROM @t WHERE ssn = T.ssn GROUP BY ssn HAVING COUNT(*) > 1)