MySQL:列出具有一个但不是另一个多对多关系的行

Question

不太确定如何询问或定义这个,但无法弄清楚.

我有三个这样的表:

persons             person_id, first_name, last_name
hobbies             hobby_id, name
persons_hobbies     person_id, hobby_id

我需要制作两个清单.既有爱好A又有B的人,以及有爱好但不爱B的人.我怎么能写出这两个问题呢？无法弄清楚如何加入和所有这一切......

说爱好A有id = 3而爱好B有id = 7.

Answer 1

这样的事情应该有效:

-- Persons that have both hobby A and B
select p.first_name,p.last_name
from persons p
inner join persons_hobbies ph1 on ph1.person_id = p.person_id and ph1.hobby_id = 3
inner join persons_hobbies ph2 on ph2.person_id = p.person_id and ph2.hobby_id = 7;

-- Persons that have hobby A but not B 
select p.first_name,p.last_name
from persons p
inner join persons_hobbies ph1 on ph1.person_id = p.person_id and ph1.hobby_id = 3
left outer join persons_hobbies ph2 on ph2.person_id = p.person_id and ph2.hobby_id = 7
where ph2.person_id is null;