Common Table Expression For Sorting Hierarchical Records By Depth

bdrajer — Thu, 26 Feb 2009 14:54:11 +0000

I tried to find this on the net, and was unable to find a satisfying and simple solution. How do you retrieve hierarchical records (say, from a self-referencing table) sorted by their depth in the hierarchy? Microsoft SQL Server 2005/2008 has a new SQL construct, Here’s one example: a Category table with an ID (primary key) and ParentID (pointing to the hierarchical parent).

WITH CategoryCTE(ID, ParentID, Depth)
AS
(
  SELECT ID, ParentID, 0
  FROM Category
  WHERE ParentID IS NULL – root records

  UNION ALL 

  SELECT cRecursive.ID, cRecursive.ParentID, cCte.Depth+1
  FROM Category AS cRecursive JOIN CategoryCTE AS cCte
      ON cRecursive.ParentID = cCte.ID
)
SELECT *
FROM CategoryCTE
ORDER BY Depth

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Common Table Expression For Sorting Hierarchical Records By Depth