加入ID如果存在其他列

Question

我有兩個現有表{PeopleList,EmployeeList}。我的問題是如何創建一個查詢連接另一個表，如果列中存在一條記錄，但如果不存在，則返回另一列的另一條記錄。爲了使它更清楚，我將在下面提供一些信息（僞記錄）：

PeopleList Table

AutoInc_ID  EmployeeID  Name 
============================================ 
1    EMP001   Mr. John Doe 
2        Mr. Johnsons 
3        Mrs. Jane Smith 
4    EMP002   Mr. Juan Dela Cruz 

和

EmployeeList Table

EmployeeID  AliasName  DepartmentID 
============================================ 
EMP001   JDoe   DEP001 
EMP002   JDCruz  DEP001 
EMP003   Alien   DEP051 

，我想結果是：

Result Table

AutoInc_ID  WorkerName 
============================================ 
1    JDoe 
2    Mr. Johnsons 
3    Mr. Jane Smith 
4    JDCruz 

Answer 1

SELECT 
    PeopleList.AutoInc_ID, 
    IFNULL(EmployeeList.AliasName,PeopleList.Name) as WorkerName 
FROM 
    PeopleList 
    LEFT JOIN EmployeeList ON PeopleList.EmployeeID=EmployeeList.EmployeeID 
;