递归 SQL 自连接

Question

我有以下员工 table 并且 EmpID 和 ManagerID 之间存在外键关系。

员工Table

期望输出

我希望能够以 > 分隔的层次顺序显示员工姓名，从最顶层的经理到最底层，EmpID 是层次结构底部的员工 ID。

我知道我可以通过使用以下 SQL.

将 table 连接到自身来获得所需的输出

select e1.empID, e1.DeptID, e2.Name + ' > ' + e1.Name as Description
from employee e1
left join employee e2
on e1.managerId = e2.empId

我也知道我可以在上面的查询中添加更多的左连接以获得所需的输出。但是层次结构的深度没有限制，所以我想它需要动态完成。

如有任何帮助，我们将不胜感激

Answer 1

您想要递归 CTE：

with e as (
      select cast(name as varchar(max)) as list, empId, 0 as level
      from employees
      where managerID is null
      union all
      select e.list + '>' + e2.name, e2.empId, level + 1
      from e join
           employees e2
           on e.empId = e2.managerId
     )
select e.*
from e
where not exists (select 1
                  from employees e2
                  where e2.managerId = e.empId
                 );

Answer 2

declare @Employees table (
    EmpId      int          ,
    DeptId     int          ,
    Name       varchar(30)  ,
    ManagerId  int
);

insert into @Employees values
( 1, 1, 'Zippy'    , 2    ),
( 2, 1, 'George'   , 3    ),
( 3, 1, 'Bungle'   , 4    ),
( 4, 1, 'Geoffrey' , null ),
( 5, 2, 'Rod'      , 6    ),
( 6, 2, 'Jane'     , 7    ),
( 7, 2, 'Freddy'   , null );

with cte as
(
    select   
        EmpId      ,
        DeptId     ,
        ManagerId  ,
        Path       =  cast('' as varchar(4000)),
        Name       ,                
        Level      =  0        
    from
        @Employees    
    where
        ManagerId is null

    union all 

    select 
        EmpId     =  e.EmpId,
        DeptId    =  e.DeptId,
        ParentId  =  e.ManagerId,
        Path      =  cast(concat(cte.Path, cte.Name, ' › ') as varchar(4000)),
        Name      =  e.Name,        
        Level     =  cte.Level + 1    
    from 
        @Employees e
        inner join cte on cte.EmpId = e.ManagerId
)
select 
    EmpId      ,
    DeptId     ,
    ManagerId  ,    
    Path       ,
    Name       ,
    FullPath   =  Path + Name,    
    Level        
from 
    cte
order by
    FullPath;

递归 SQL 自连接

Recursive SQL self join

sql

tsql

join

self-join

sql-server-2012