How to show expanding hierarchies by using SQL Server

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Summary

Databases frequently store hierarchical information. For more details about hierarchical information, see the "Expanding Hierarchies" topic in Microsoft SQL Server Books Online. The "Expanding Hierarchies" topic has a detailed Transact-SQL procedure that expands an encoded hierarchy to any arbitrary depth.

NOTE: The SQL Books Online procedure declares @level, which is a reserved word in SQL Server 6.5 and SQL Server 7.0. Level is no longer a reserved word in SQL Server 2000 and in SQL Server 2005. The following code is a corrected version of this procedure in which @lvl is substituted for the reserved word so that it works on all versions. The procedure is enhanced to include the CREATE TABLE statement, CREATE INDEX samples, and INSERT statements that are required to demonstrate the example.


Following is the updated code sample:

CREATE TABLE hierarchy
(parent VARCHAR(20) NOT NULL,
child VARCHAR(20),
CONSTRAINT UIX_parentchild
UNIQUE NONCLUSTERED (parent,child)
)
CREATE CLUSTERED INDEX CIX_parent
ON hierarchy(parent)
GO
INSERT hierarchy VALUES('World','Europe')
INSERT hierarchy VALUES('World','North America')
INSERT hierarchy VALUES('Europe','France')
INSERT hierarchy VALUES('France','Paris')
INSERT hierarchy VALUES('North America','United States')
INSERT hierarchy VALUES('North America','Canada')
INSERT hierarchy VALUES('United States','New York')
INSERT hierarchy VALUES('United States','Washington')
INSERT hierarchy VALUES('New York','New York City')
INSERT hierarchy VALUES('Washington','Redmond')
GO

CREATE PROCEDURE expand (@current char(20)) as--This is a non-recursive preorder traversal.
SET NOCOUNT ON
DECLARE @lvl int, @line char(20)

CREATE TABLE #stack (item char(20), lvl int)--Create a tempory stack.
INSERT INTO #stack VALUES (@current, 1)--Insert current node to the stack.
SELECT @lvl = 1
WHILE @lvl > 0--From the top level going down.
BEGIN
IF EXISTS (SELECT * FROM #stack WHERE lvl = @lvl)
BEGIN
SELECT @current = item--Find the first node that matches current node's name.
FROM #stack
WHERE lvl = @lvl

SELECT @line = space(@lvl - 1) + @current--@lvl - 1 s spaces before the node name.
PRINT @line--Print it.

DELETE FROM #stack
WHERE lvl = @lvl
AND item = @current--Remove the current node from the stack.

INSERT #stack--Insert the childnodes of the current node into the stack.
SELECT child, @lvl + 1
FROM hierarchy
WHERE parent = @current

IF @@ROWCOUNT > 0--If the previous statement added one or more nodes, go down for its first child.
SELECT @lvl = @lvl + 1--If no nodes are added, check its brother nodes.
END
ELSE
SELECT @lvl = @lvl - 1--Back to the level immediately above.

END --While

GO
EXEC expand 'World'


The result is World North America United States Washington Redmond New York New York City Canada Europe France Paris

References

For additional information, see the "Expanding Hierarchies" topic in Microsoft SQL Server Books Online.

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ID članka: 248915 - posljednja izmjena: 12. ruj 2008. - verzija: 1

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