SQL查询的帮助 - 没有关系，找到行

Question

考虑与客户端表和书籍表一个DB：

客户：PERSON_ID

书：book_id

Client_Books：为person_id，book_id

你会如何找到所有没有书的Person ID？ （没有做外连接和寻找空值）

Answer 1

select * 
from Client 
where person_id not in (select person_id from Client_Books) 

Answer 2

select * 
from Client as c 
where not exists(select * from Client_Books where person_id =c.person_id) 

Answer 3

SELECT * FROM Client WHERE person_id not in (SELECT person_id FROM Client_Books) 

Answer 4

select * 
from Client as c 
where (select coun(*) from Client_Books where person_id =c.person_id) = 0 

COUNT的完整性，因为有已经存在，并且在解决方案发布。