Hierarchical Tree Structures in Database Tables

This recursive function retrieves a hierarchical tree structure from a table with just four columns that describe each node in the tree: Level (the depth of the node in the tree), ID, Name, and ParentID. Given an ID and a Level, the function opens a cursor and retrieves the entire branch of the tree for the specified node at that level.

First, create the table:

Create Table Tree(ID int,Name Varchar(10),ParentID int)Go

Next, create the function:

Create Function getTree(@ID Int,@Level int=1)Returns @Tree Table(Level int,ID int,Name Varchar(10),ParentID int)AsBegin	Declare @tID int,@tName Varchar(10),@tParentID int	Declare TreeCur Cursor	For	Select * From Tree Where [email protected]	Open TreeCur	FETCH NEXT FROM TreeCur into @tID,@tName,@tParentID	Insert Into @Tree Select @Level,* From Tree Where [email protected]	Set @[email protected]+1	WHILE (@@fetch_status = 0)	Begin		Insert Into @Tree Select * From dbo.getTree(@tID,@Level)		FETCH NEXT FROM TreeCur into @tID,@tName,@tParentID	End	Close TreeCur	Deallocate TreeCur	returnEnd

Lastly, fill the table:

INSERT INTO Tree  VALUES(1,'Root',0)GoINSERT INTO Tree  VALUES(2,'Node 1',1)GoINSERT INTO Tree  VALUES(3,'Node 2',1)GoINSERT INTO Tree  VALUES(4,'Node 1.1',2)GoINSERT INTO Tree  VALUES(5,'Node 1.2',2)GoINSERT INTO Tree  VALUES(6,'Node 1.1.1',4)GoINSERT INTO Tree  VALUES(7,'Node 2.1',3)GoBuild the tree using Function

To get the tree built from the root, use this:

select * from getTree(1,DEFAULT)Level       ID          Name       ParentID    ----------- ----------- ---------- ----------- 1           1           Root       02           2           Node 1     13           4           Node 1.1   24           6           Node 1.1.1 43           5           Node 1.2   22           3           Node 2     13           7           Node 2.1   3(7 row(s) affected)

To retrieve the tree built from Node 1, use:

select * from getTree(2,DEFAULT)Level       ID          Name       ParentID    ----------- ----------- ---------- ----------- 1           2           Node 1     12           4           Node 1.1   23           6           Node 1.1.1 42           5           Node 1.2   2(4 row(s) affected)

To retrieve the tree built from Node 2, use:

select * from getTree(3,DEFAULT)Level       ID          Name       ParentID    ----------- ----------- ---------- ----------- 1           3           Node 2     12           7           Node 2.1   3(2 row(s) affected)
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