仅使用主键和外键获取值

Question

我已经尝试了几个queries和joins，我无法解决这个问题。

我有2个表

Employee 
-------- 
ID(PK)                                  
Firstname                                     
Lastname                                     
ContactNumber                                     
Position                   
TeamleaderID(FK) //*which is only applicable if the position isn't a team leader*// 

Team Leader 
---------- 
ID(PK)                   
employeeID(FK) 

Employee表由2个数据，所述第一个是。

ID(PK) - 1                   
Firstname - Mikael                                
Lastname - Roque                              
ContactNumber - 0010101                            
Position - TeamLeader                                                
TeamleaderID(FK) - Null 

：第二个是

ID(PK) - 2                   
Firstname - Rinnie                   
Lastname - Hoshino                   
ContactNumber - 0010101                   
Position - Engineer                   
TeamleaderID(FK) - 1 

第三届一种是为teamleader表

ID(PK) - 1                   
employeeID(FK) - 1 

我已经试过此查询

SELECT employee.*                   
FROM employee                   
JOIN teamleader                   
ON employee.teamleader_id=teamleader.teamleader_id                   
Where employee.firstname='Rinnie'; 

但结果是teamleader id仅显示。是否可以选择所有employee数据，包括teamleader的名称？

Answer 1

请尝试查询如图所示。您发布的查询的问题是，您并未选择团队领导者的姓名，而只是原来的员工。为了获得团队领导者的姓名，您必须加入员工表的另一个实例（employee_1），并链接到表teamleader中的employeeId字段。

SELECT e.*, m.FirstName as TeamLead 
FROM employee e 
join teamlead on e.TeamleaderId = teamlead.ID 
join employee m on teamlead.employeeID = m.ID 
WHERE e.FirstName = "Rinnie"; 

干杯，

Answer 2

您需要另一个加盟用于获取结果：

SELECT employee.*,leader.* 
FROM employee 
LEFT JOIN teamleader ON employee.teamleader_id=teamleader.teamleader_id 
LEFT JOIN employee as leader ON teamleader.employeeID = leader.ID 
Where employee.firstname='Rinnie'; 

我加左加入了employeee没有teamleader。