多对多查询MySQL

Question

我有两个表：用户[id，email]和角色[id，name]与多对多连接表user_has_roles [user_id，role_id]。 我试图让这显示哪些用户具有特定角色表，如果没有的话空（或0）类似如下：

  | role 1 | role 2 | role 3 
--------------------------------------- 
user1@email | 1  | null | 1 
user2@email | null | null | 1 
--------------------------------------- 

感激有这方面的帮助。

Answer 1

select u.email, 
     case when sum(r.name = 'role 1') > 0 then 1 else null end as `role 1`, 
     case when sum(r.name = 'role 2') > 0 then 1 else null end as `role 2`, 
     case when sum(r.name = 'role 3') > 0 then 1 else null end as `role 3` 
from users u 
left join user_has_roles ur on ur.user_id = u.id 
left join roles r on ur.role_id = r.id 
group by u.email