MySQL数据查询(多表)

有AB两表，A表主码为c_id，B表外码p_c_id参照c_id，查询c_id，条件是没有p_c_id与之相等

方式1：
select
c_id
from A a
left join B b
on a.c_id = b.p_c_id
where b.p_c_id is null;

方式2：
select c_id from A where c_id not in
(select p_c_id from B)；

select c_id from A where c_id not in
(select p_c_id from B)；

或者

select c_id from A,B where c_id != p_c_id;