使用SQL進行多對多查詢

Question

EmployeeGroups有許多MedicalPlans。 MedicalPlans有許多EmployeeGroups（多對多關係）。它們連接雖然EmployeeBenefits連接表

EmployeeGroup 
:id 
:name 

MedicalPlan 
:id 
:name 

EmployeeBenefits 
:id 
:employee_group_id 
:medical_plan_id 

有誰知道查詢我可以用它來獲取所有誰有一定MedicalPlan的EmployeeGroups？

我不相信INNER JOIN在這裏工作，因爲他們沒有共同的屬性。任何幫助，將不勝感激！

Answer 1

是，內連接工程

select eg.name 
from EmployeeGroup eg 
join EmployeeBenefits eb on eb.employee_group_id = eg.id 
join MedicalPlan mp on eb.medical_plan_id = mp.id 
where mp.name = 'my plan' 

Answer 2

使用EXISTS或IN這樣的任務：

select * 
from employeegroup 
where id in 
(
    select employee_group_id 
    from employeebenefits 
    where medical_plan_id = (select id from medicalplan where name = 'XYZ') 
);