SQlite如何在此表中顯示員工和經理姓名？

Question

我是SQLite新手。我想顯示每個員工的姓名和他/她的經理姓名。但是我對如何將managerID與EmployeeID關聯有點困惑？我需要使用子查詢嗎？

table: Employee 
Columns: EmployeeID [pk], EmployeeName, ManagerID 

像：

EmployeeID EmployeeName ManagerID 
    1    Alice   2 
    2    Peter   null 
    3    John   2 
    4    Mary   1 

意味着彼得是Alice和John的經理和Alice是瑪麗的經理。

SELECT EmployeeName AS Employee, EmployeeName AS Manager 
FROM Employee 
WHERE 

Answer 1

您需要自行加入表格LEFT OUTER join。由於老闆不會有經理（空），因此請使用'ifnull'：

select A.EmployeeName as 'EmployeeName', 
    ifnull(B.EmployeeName, 'BOSS') as 'ManagerName' 
    from employee A left outer join employee B 
    on A.managerId = B.employeeId;