使用自联接或任何其他方式识别结果的SQL查询

Question

假设我有一个如下表：

ID  Name    ManagerID

1   Dave       NULL

2   Scott       1

3   Mike        1

4   Nick        3

5   Jack        1

如何查找所有员工的相应经理姓名，如下面的格式？

ID  Name    ManagerID   ManagerName

1   Dave    NULL        NULL

2   Scott   1           Dave

3   Mike    1           Dave

4   Nick    3           Mike

5   Jack    1           Dave

Answer 1

试试这个！

select a.ID,a.Name,a.ManagerID,b.Name as ManagerName 
       from #t a left join #t b on a.ManagerID=b.ID 

Demo

Answer 2

select ID, Name, ManagerID,
       (case when managerid is null then null else (select Name from tab where id=managerid) end) as ManagerName
from tab

你也可以这样做

Answer 3

可能有多种方式。 如：

SELECT 
    ID, Name, ManagerID, 
    (SELECT Name FROM table AS ManagersTable WHERE ManagersTable.ID=EmployeesTable.ManagerID) AS ManagerName
FROM table AS EmployeesTable