SQL Server: Grouping heirarchical data - sql

Question

I have a document table - see below for definition
In this table We have a root document which has a OriginalDocID of null
Every time a revision is made a new entry is added with the parents documentID as the OriginalDocID
What I am looking to do is to be able to group/partition everything around the Original document that has OriginalDocID of null
Each document can have multiple revisions from one point of origin.
meaning we can have
Doc Id 1 -> 2 -> 3
2 -> 8 -> 9
1 -> 4 -> 7
5 -> 10
So what I would hope to see back is all the rows with the root document. appended
I hope this makes sense. For the life of me I can't wrap my head around a sufficient query.
CREATE TABLE [dbo].[Document](
[DocumentID] [int] IDENTITY(1,1) NOT NULL,
[DocumentName] [varchar](max) NOT NULL,
[ContentType] [varchar](50) NULL,
[DocumentText] [varchar](max) NULL,
[DateCreated] [datetime] NULL,
[DocumentTypeId] [int] NULL,
[Note] [varchar](8000) NULL,
[RefID] [int] NULL,
[Version] [int] NULL,
[Active] [bit] NULL,
[OriginalDocID] [int] NULL
)

Answer 1

You'll need to use a Recursive CTE to do this. That's a query that refers back to itself so it can traverse a hierarchy and gather information as it works it's way down (or up) the levels of that hierarchy.
In your case, something like:
WITH RECURSIVE docCTE AS
(
/* Recursive Seed */
SELECT
cast(null as int) as parentdoc
documentID,
0 as depth,
documentid as originalDocument,
CAST(null as varchar(100) as docpath
FROM
dbo.document
Where originalDocID IS NULL
UNION ALL
/* Recursive Term */
SELECT
docCTE.DocumentID as parentdoc,
document.documentID,
depth + 1 as depth,
docCTE.originalDocument,
docCTE.Path + '>' + document.documentID
FROM
docCTE
INNER JOIN dbo.document on doccte.document = document.originalDocID
WHERE
depth <= 15 /*Keep it from cycling in case of bad hierarchy*/
)
SELECT * FROM docCTE;
The recursive CTE is made up of two parts.
The recursive seed, which is what we use to kick of the query. This is all document records where the originalDocID is null.
The recursive term, where we join the table back to the recursive CTE establishing the parent/child relationship.
In your case we capture the documentid in the Recursive Seed as the originalDoc so that we can bring that down through each record found when we start traversing the hierarchy of documents.
These can be a little overwhelming when you get started, but after you write it a few times, it's second nature (and you'll find the really really helpful as you encounter more of this type of data).