Need a query to insert 'level' into an adjacent list - sql

Question

I have a table like so
ID Node ParentID
1 A 0
2 B 1
3 C 1
4 D 2
5 E 2
6 F 3
7 G 3
8 H 3
9 I 4
10 J 4
11 K 10
12 L 11
I need a query to generate a 'level' field that shows how many levels deep a particular node is. Example below
ID Node ParentID Level
1 A 0 1
2 B 1 2
3 C 1 2
4 D 2 3
5 E 2 3
6 F 3 4
7 G 3 4
8 H 3 4
9 I 4 5
10 J 4 5
11 K 10 6
12 L 11 7

Answer 1

Select Id,
Node,
ParentID,
Dense_Rank() Over(Order by ParentID) as Level
from Table_Name
SQL Fiddle Demo

Answer 2

You can use DENSE_RANK function
SELECT i.ID, p.Node, i.ParentID
,Dense_Rank() Over(Order by ParentID) as Level
FROM TableName AS i;
for more detail visit: http://blog.sqlauthority.com/2007/10/09/sql-server-2005-sample-example-of-ranking-functions-row_number-rank-dense_rank-ntile/

Answer 3

I think the correct way to do it will be to get the parent level and increment it by 1 when inserting the data since all other ways are expensive performance wise.

Answer 4

Something like:
;with tree (ID, ParentID, Level)
as (
select ID, ParentID, 1 from TableName where ParentID = 0
union all
select t.ID, t.ParentID, 1 + tree.Level
from Tree join TableName t on t.ParentID = Tree.ID
)
select ID, Level from Tree

Answer 5

Try this
CREATE TABLE #Table1
([ID] int, [Node] varchar(1), [ParentID] int)
;
INSERT INTO #Table1
([ID], [Node], [ParentID])
VALUES
(1, 'A', 0),
(2, 'B', 1),
(3, 'C', 1),
(4, 'D', 2),
(5, 'E', 2),
(6, 'F', 3),
(7, 'G', 3),
(8, 'H', 3),
(9, 'I', 4),
(10, 'J', 4),
(11, 'K', 10),
(12, 'L', 11)
;
;WITH CTE ([ID], [ParentID], [Node], [Level])
as (
SELECT [ID], [ParentID], [Node], 1 FROM #Table1 WHERE ParentID = 0
UNION all
select t.[ID], t.[ParentID], t.[Node], 1 + c.[Level]
from CTE c inner join #Table1 t ON t.[ParentID] = c.[ID]
)
select ID, [Node], [ParentID], [Level] from CTE
ORDER BY [Node]
DROP TABLE #Table1

Answer 6

Here, you need to set level by grouping ParentID then join both tables by ParentID.
WITH CTE (ParentID, Level)
AS (
SELECT ParentID
, Row_Number() OVER (ORDER BY ParentID) AS Level
FROM Table1
GROUP BY ParentID
)
SELECT t1.ID, t1.Node, t1.ParentID, CTE.Level
FROM Table1 t1
JOIN CTE ON t1.ParentID = CTE.ParentID;
See this SQLFiddle
Update: (for MySQL - just to help others)
To do the same in MySQL try to get row number like this:
SELECT t1.ID, t1.Node, t1.ParentID, Tbl.Level
FROM Table1 t1
JOIN
(
SELECT #Level:=#Level+1 AS Level , ParentID
FROM (SELECT DISTINCT ParentID FROM Table1) t
, (SELECT #Level:=0) r
ORDER BY ParentID
) Tbl
ON t1.ParentID = Tbl.ParentID;
See this SQLFiddle