Question

I am using SQL Server 2008 and have a SQL challenge I have never run into before. Consider the following table that represents a hierarchical category list:

ID  Name            Description                     ParentID
--- --------------- ------------------------------- --------
1   Bicycle         Bicycles and Tricycles          {null}
2   Wheels          Wheels                          1
3   Spoked          Spoked Wheels                   2
4   Skate Boards    Skate Boards and accessories    {null}
5   Wheels          Skate Board Wheels              4
6   Polyurethane    Polyurethane Wheels             5

Results I am looking for:

ID  Heirarchy                               Description
--- --------------------------------------- ------------------------------------
1   Bicycle                                 Bicycles and Tricycles
2   Bicycle, Wheels                         Wheels
3   Bicycle, Wheels, Spoked                 Spoked Wheels
4   Skate Boards                            Skate Boards and accessories
5   Skate Boards, Wheels                    Skate Board Wheels
6   Skate Boards, Wheels, Polyurethane      Polyurethane Wheels

I would like to Query this table and return a name for each row that would represent the hierarchy by concatenating the name(s) of each parent to the child. The hierarchy does not have a pre-set nesting depth and I would like to be able to run this in a single query. How can this be accomplished?

Answer 1

with tree as (
   select id, 
          cast(name as varchar(max)) as hierarchy,
          name, 
          description
   from the_table
   where parentID is null
   union all
   select c.id, 
          p.hierarchy + ', ' + c.name,
          c.name,
          c.description
    from the_table c
       join tree p on p.id = c.parentID
) 
select * 
from tree;