sqlsql-serversql-server-2008-r2hierarchy

How can I generate a hierarchy path in SQL that leads to a given node?


In my MS SQL 2008 R2 database I have this table:

TABLE [Hierarchy]
[ParentCategoryId] [uniqueidentifier] NULL,
[ChildCategoryId] [uniqueidentifier] NOT NULL

I need to write a query that will generate all paths that lead to a given Node.

Lets say it I have the following tree:

A
-B
--C
-D
--C

Which would be stored as:

NULL | A
A    | B
A    | D
B    | C
D    | C

When asking for the Paths for C, I would like to get back two paths (written more or less like this):

A > B > C,
A > D > C

Solution

  • Here is my solution, Sql Fiddle

    DECLARE @child VARCHAR(10) = 'C'
    
        ;WITH children AS
        (
    
           SELECT 
             ParentCategoryId,
            CAST(ISNULL(ParentCategoryId + '->' ,'')  + ChildCategoryId AS VARCHAR(4000)) AS Path
           FROM Hierarchy
           WHERE ChildCategoryId =  @child
         UNION ALL
           SELECT 
             t.ParentCategoryId,
             list= CAST(ISNULL(t.ParentCategoryId  + '->' ,'')  + d.Path AS VARCHAR(4000))
           FROM Hierarchy t
           INNER JOIN children  AS d
                ON t.ChildCategoryId = d.ParentCategoryId
         )
    
        SELECT Path 
        from children c
        WHERE ParentCategoryId IS NULL
    

    Output:

    A->D->C 
    A->B->C 
    

    UPDATE:

    @AlexeiMalashkevich, to just get id, you may try this

    SQL Fiddle

    DECLARE @child VARCHAR(10) = 'C'
    
    ;WITH children AS
    (
    
       SELECT 
         ParentCategoryId,
         ChildCategoryId  AS Path
       FROM Hierarchy
       WHERE ChildCategoryId =  @child
     UNION ALL
       SELECT 
         t.ParentCategoryId,
         d.ParentCategoryId 
       FROM Hierarchy t
       INNER JOIN children  AS d
            ON t.ChildCategoryId = d.ParentCategoryId
     )
    
    SELECT DISTINCT PATH
    from children c