Tables for recursive hierarchial data in SQL [duplicate] - sql

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Simplest way to do a recursive self-join in SQL Server?
I have to create a table in SQL that will comprise of groups of items/products. Each new group made will be made under one of the pre-defined groups or the groups previously formed. I want to keep all this data in a SQL Table. So far, I have though of creating a table like this:
Group ID
Group Name
Group Under (This will store the ID of the group under which this group is from
But this can only refer to just the next level, how will I get to know who is the super-parent of this group.
For example:
I have groups A, B, C.
A has further subgroups A1, A2, A3.
A1 has further subgroups, A11, A12, A13.
I will I have the information about super-parent group i.e A from A11 or A22 or A33?
Let me know if the problem is not clear..

Answer 1

Assuming T-SQL and MSSQLServer (you didn't specify), and given that your Group table should look something like this:
Id | Name | ParentId
---+------+---------
1 | A | NULL
2 | B | NULL
3 | C | NULL
4 | A1 | 1
5 | A2 | 1
6 | A3 | 1
7 | A11 | 4
8 | A12 | 4
9 | A13 | 4
You can use the following recursive CTE to find the top level a given group, say 'A12':
WITH [Group](Id, Name, ParentId) AS
(
SELECT 1, 'A' , NULL UNION
SELECT 2, 'B' , NULL UNION
SELECT 3, 'C' , NULL UNION
SELECT 4, 'A1' , 1 UNION
SELECT 5, 'A2' , 1 UNION
SELECT 6, 'A3' , 1 UNION
SELECT 7, 'A11', 4 UNION
SELECT 8, 'A12', 4 UNION
SELECT 9, 'A13', 4
), q AS
(
SELECT
*
FROM
[Group]
WHERE
[Name] = 'A12' -- Given 'A12' as the child
UNION ALL
SELECT
g.*
FROM
[Group] g
JOIN
q
ON
q.ParentId = g.Id
)
SELECT
*
FROM
q
WHERE
ParentId IS NULL
This query returns:
Id | Name | ParentId
---+------+---------
1 | A | NULL