Question

I have a emp table,

    CREATE TABLE [dbo].[Emp](
    [EmpId] [int] NULL,
    [EmpName] [nvarchar](50) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
    [ManagerId] [int] NULL
) ON [PRIMARY]

Now, insert below values into the table

   Insert Into Emp Values(1,'A',0)
Insert Into Emp Values(2,'B',1)
Insert Into Emp Values(3,'C',2)
Insert Into Emp Values(4,'D',2)
Insert Into Emp Values(5,'E',4)
Insert Into Emp Values(6,'F',4)
Insert Into Emp Values(7,'G',4)
Insert Into Emp Values(8,'H',6)
Insert Into Emp Values(9,'I',5)
Insert Into Emp Values(10,'J',7)
Insert Into Emp Values(11,'K',4)

I want to list employee name and their manager name in select statement.

What I am doing now is creating a temporary table which has all manager name and their Id.

Then getting the name from the manager table based on Id.

But I know this is not a correct way, in fact it is complex.

Answer 1

You should use a recursive CTE (Common Table Expression) for this:

-- define the recursive CTE and give it a name
;WITH Hierarchy AS
(
    -- "anchor" - top-level rows to select, here those with ManagerId = 0
    SELECT EmpId, EmpName, NULL AS 'MgrId', CAST(NULL AS NVARCHAR(50)) AS 'MgrName', 1 AS 'Level'
    FROM dbo.Emp
    WHERE ManagerId = 0

    UNION ALL

    -- recursive part - join an employee to its manager via ManagerId -> mgr.EmpId
    SELECT e.EmpId, e.EmpName, mgr.EmpId, mgr.EmpName, mgr.Level + 1 AS 'Level'
    FROM dbo.Emp e
    INNER JOIN Hierarchy mgr ON e.ManagerId = mgr.EmpId
)
SELECT * FROM Hierarchy