Get hierarchical structure using SQL Server

Question

I have a self-referencing table with a primary key, id and a foreign key parent_id.

+------------+--------------+------+-----+---------+----------------+
| Field      | Type         | Null | Key | Default | Extra          |
+------------+--------------+------+-----+---------+----------------+
| id         | int(11)      | NO   | PK  | NULL    | IDENTITY       | 
| parent_id  | int(11)      | YES  |     | NULL    |                | 
| name       | varchar(255) | YES  |     | NULL    |                | 
+------------+--------------+------+-----+---------+----------------+

I have got a table as following (reduce data for more clear)

Table MySiteMap

  Id   Name  parent_id
   1    A    NULL
   2    B    1
   3    C    1
   4    D    1

  20    B1   2  
  21    B2   2

  30    C1   3
  31    C2   3

  40    D1   4
  41    D2   4

I would like get the hierarchical structure using SQL Server query:

  A 
  |
   B
    |
    |  B1
    |  B2
   C
    |
    |  C1
    |  C2
   D
    |
    |  D1
    |  D2

Any suggestions?

Answer 1

You can use Common Table Expressions.

WITH LeveledSiteMap(Id, Name, Level)
AS
(
    SELECT Id, Name, 1 AS Level
    FROM MySiteMap
    WHERE Parent_Id IS NULL
    UNION ALL
    SELECT m.Id, m.Name, l.Level + 1
    FROM MySiteMap AS m
        INNER JOIN LeveledSiteMap AS l
        ON m.Parent_Id = l.Id
)
SELECT *
FROM LeveledSiteMap

Answer 2

Use this:

;WITH CTE(Id, Name, parent_id, [Level], ord) AS (
    SELECT 
        MySiteMap.Id, 
        CONVERT(nvarchar(255), MySiteMap.Name) AS Name, 
        MySiteMap.parent_id, 
        1,
        CONVERT(nvarchar(255), MySiteMap.Id) AS ord
    FROM MySiteMap
    WHERE MySiteMap.parent_id IS NULL
    UNION ALL
    SELECT 
        MySiteMap.Id, 
        CONVERT(nvarchar(255), REPLICATE(' ', [Level]) + '|' + REPLICATE(' ', [Level]) + MySiteMap.Name) AS Name, 
        MySiteMap.parent_id, 
        CTE.[Level] + 1,
        CONVERT(nvarchar(255),CTE.ord + CONVERT(nvarchar(255), MySiteMap.Id)) AS ord
    FROM MySiteMap
        JOIN CTE ON MySiteMap.parent_id =CTE.Id
    WHERE MySiteMap.parent_id IS NOT NULL
)
SELECT Name
FROM CTE
ORDER BY ord

For this:

A
 | B
  |  B1
  |  B2
 | C
  |  C1
  |  C2
 | D
  |  D1
  |  D2