僅使用主鍵和外鍵獲取值

Question

我已經嘗試了幾個queries和joins，我無法解決這個問題。

我有2個表

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個數據，所述第一個是。

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

：第二個是

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

第三屆一種是爲teamleader表

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

我已經試過此查詢

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

但結果是teamleader id僅顯示。是否可以選擇所有employee數據，包括teamleader的名稱？

Answer 1

請嘗試查詢如圖所示。您發佈的查詢的問題是，您並未選擇團隊領導者的姓名，而只是原來的員工。爲了獲得團隊領導者的姓名，您必須加入員工表的另一個實例（employee_1），並鏈接到表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"; 

乾杯，

Answer 2

您需要另一個加盟用於獲取結果：

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沒有teamleader。