SELECT在单个表中具有一行的祖父级-SQL

Question

I have a table with following hypothetical data:

ID | Name    | managerId
---|---------|-----------
1  | James   | 2
2  | Martin  | 4
3  | Huges   | 5
4  | Richard | NULL
5  | Kavin   | 4
6  | Rita    | 3

In the above table we have:

Richard is manager of Martin is manager of James.

Richard is manager Kavin is manager of Huges is manager of Rita.

Now I have to select immediate manager and grand manager of an employee in this table. I mean if we start from Rita I have to select Huges (immediate manager) and Richard (grand manager).

How to do that. I have no clue at all.

EDIT :
There isn't any specific levels of managers. An Employee can have 'n' Number for managers in hierarchy where n ϵ {0,1,2,3.....}

Answer 1

Because you only need two levels, this is quite feasible to do this with a self join, twice. Also, you probably want left join :

select t.*, tm.name as managername, tmm.name as manager_managername
from t left join
     tm
     on t.managerId = tm.id left join
     tmm
     on tm.managerId = tmm.id;

You can add where t.name = 'Rita' .

If you have to do this up to any level, then you should definitely review this question . The short answer is that you probably need another data structure to handle this type of query in MySQL.

Answer 2

EDIT:

The following answer works only for a specific level of parents (as question was asking before the change). I am sure that for N levels it needs a completely different approach.

You can use this. It's going up to three levels of managers and finds all employees who have at least 2 levels of managers.

SELECT aa.Name AS employee, bb.Name AS parent_manager, cc.Name AS grandparent_manager, dd.Name AS grand_grandparent_manager
FROM t1 AS aa
INNER JOIN t1 AS bb
ON aa.managerId = bb.ID
INNER JOIN t1 AS cc
ON bb.managerId = cc.ID
LEFT JOIN t1 AS dd
ON cc.managerId = dd.ID

And this is if you want the managers for a specific employee.

SELECT aa.Name AS employee, bb.Name AS parent_manager, cc.Name AS grandparent_manager, dd.Name AS grand_grandparent_manager
FROM t1 AS aa
INNER JOIN t1 AS bb
ON aa.managerId = bb.ID
INNER JOIN t1 AS cc
ON bb.managerId = cc.ID
LEFT JOIN t1 AS dd
ON cc.managerId = dd.ID
WHERE aa.Name = 'Rita'