SQL query: help needed

Question

I need help with a sql query, I have tried to replicate my actual problem by creating this simple example:

Parents table:

id   name     parent_id
1   parent1     null
2   parent2     1
3   parent3     1
4   parent4     3
5   parent5     3
6   parent6     5
7   parent7     5

Relatives table:

id    name       parent_id
1   relative1   2
2   relative2   3
3   relative3   4
4   relative4   5
5   relative5   7

Parents table has a list of parents which also have parents themselves. Relatives table has a list of relatives with a parent_id column.

How would I find all the relatives of parent3 including all the 'desendants' of parent3, ie the query should return the following from the Relatives table:

relative2 (because the parent id is 3)

relative3 (because the parent id is 4 whose parent id is 3)

relative4 (because the parent id is 5 whose parent id is 3)

relative5 (because the parent id is 7 whose parent id is 5 whose parent id is 3)

I'm using SQL Server 2008. Hope that makes sense, any help is appreciated.

Answer 1

Try this

;WITH CTE
AS
(
    SELECT [id], [name] FROM  Parents WHERE [name] = 'parent3'
    UNION ALL
    SELECT T1.[id], T1.[name] FROM CTE c 
    INNER JOIN  Parents T1 ON c.[id] = T1.[parent_id]
)

SELECT * FROM Relatives 
WHERE [parent_id] IN (SELECT [id] FROM CTE)

SQL FIDDLE DEMO