I have a database containing a hierarchy of categories stored using the adjacency list model.
The hierarchy is 3 levels deep (not including an imaginary root node) and contains approx 1700 nodes. Nodes in the 2nd and 3rd levels can have multiple parents. A additional table is used for the many-to-many relationship as below:
CREATE TABLE dbo.Category(
id int IDENTITY(1,1) NOT NULL,
name varchar(255) NOT NULL,
)
CREATE TABLE dbo.CategoryHierarchy(
relId int IDENTITY(1,1) NOT NULL,
catId int NOT NULL,
parentId int NOT NULL,
)
If I move to using the transitive closure table method (for the sake of data integrity etc) is there a relatively easy query I can execute that would generate the values for the closure table? (using SQL Server 2005)
I've look through articles and presentations such as Bill Karwin's Models for hierarchical data but that only has insertion queries for a single node and it would take forever for me to create my tree like that.
Thanks.
EDIT:
RelID in the CategoryHierarchy table is purely for the sake of a primary key, it has no bearing on the node ids of the Category table.
Also by closure table, I mean a table like this:
CREATE TABLE ClosureTable (
ancestor int NOT NULL,
descendant int NOT NULL,
[length] int NOT NULL,
)
Where the first two columns are a compound primary key, and are individually foreign keys to Category.id.
I was trying to figure out the same thing, but wanted it in a recursive CTE. This wouldn't have worked for you (SQL Server 2008+), but here's what I ended up with for anyone else looking.
The key is that the anchors aren't your root nodes (where parent_id IS NULL
), but instead all your zero depth rows-to-be in the closure table.
CREATE TABLE dbo.category (
id INT IDENTITY(1, 1) NOT NULL,
parent_id INT NULL
)
INSERT INTO dbo.category (id, parent_id)
VALUES
(1, NULL),
(2, 1),
(3, 1),
(4, 2)
WITH category_cte AS
(
SELECT
id AS ancestor,
id AS descendant,
0 AS depth
FROM dbo.category
UNION ALL
SELECT
CTE.ancestor AS ancestor,
C.id AS descendant,
CTE.depth + 1 AS depth
FROM dbo.category AS C
JOIN category_cte AS CTE
ON C.parent_id = CTE.descendant
)
SELECT * FROM category_cte
ancestor descendant depth
-------- ---------- -----
1 1 0 <- anchor query
2 2 0
3 3 0
4 4 0
2 4 1 <- first recursive query
1 2 1
1 3 1
1 4 2 <- second recursive query
I think I've been able to work out the solution myself.
If anyone has a better way of doing this, please comment.
IF OBJECT_ID('dbo.ClosureTable', 'U') IS NOT NULL
DROP TABLE dbo.ClosureTable
GO
CREATE TABLE dbo.ClosureTable (
ancestor int NOT NULL,
descendant int NOT NULL,
distance int NULL
)
GO
DECLARE @depth INT
SET @depth = 1
INSERT INTO dbo.ClosureTable (ancestor, descendant, distance)
SELECT catid, catid, 0 FROM dbo.Category -- insert all the self-referencing nodes
WHILE (@depth < 4) -- my tree is only 4 levels deep, i.e 0 - 3
BEGIN
INSERT INTO dbo.ClosureTable (ancestor, descendant, distance)
SELECT ct.ancestor, h.catid, @depth
FROM dbo.ClosureTable ct INNER JOIN dbo.CategoryHierarchy h ON ct.descendant = h.parentid
WHERE ct.distance = @depth - 1
SET @depth = @depth + 1
END
Cheers :)
WITH Children (id, name, iteration) AS (
SELECT id, name, 0
FROM Category
--WHERE id = @folderid -- if you want a startpoint
UNION ALL
SELECT b.id, b.name, a.iteration + 1
FROM Children AS a, Category AS b, CategoryHierarchy c
WHERE a.id = c.parentId
AND b.id = c.catId
)
SELECT id, name, iteration FROM Children
Not tested, but should work like this. At least a start how you do this fast without loops.
EDIT: I missred, not relId, it is parentId that has to link to Childrens table. But the result should be a table with all tables. So this is not what your originally wanted?
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