[LeetCode 607] Sales Person

'RED' 회사와 일하지 않은 사람 id를 반환하자.

 간단하게 join해서 풀 수 있다. 

select name
from salesperson 
where sales_id not in 
    (select o.sales_id
    from orders as o join
        company as c on o.com_id = c.com_id
    where c.name = 'RED') ;

아래는 처음 제출한 코드. join이 하나 필요 없어서 뺐는데 왜 이 코드가 더 빠른 걸까. 

select d.name
from salesperson as d
where d.sales_id not in 
    (select o.sales_id
    from salesperson as s join
        orders as o on o.sales_id = s.sales_id join
        company as c on o.com_id = c.com_id
    where c.name = 'RED') ;