SQL Query / Herigate data join - sql

Question

I have two tables, the first with person data
ID
Name
The second has each person relatives
Primary Key Field
Person (references person.id)
RelativeType (mother or father)
Parent (references person.id)
I'm trying to get all the sons and grandsons of a specific person and I'm stuck integrating the grandsons in the query results. I'm using SQL Server.
Any ideas?

Answer 1

The query you need depends highly of how many level you have of the Parent-Child relationship. If you can change the schema, I would recommend you turn into using HierarchyId which is an SQL Server specific data type. Have a look here.
In the following, I assume you only have 2 levels. Father - Son - GrandSon
;WITH Sons AS (
SELECT pdf.Id, pdf.Name, pdd.Id ParentId, pdd.Name Parent FROM PersonData pdf
JOIN PersonRelative pr ON pdf.Id = pr.Parent
JOIN PersonData pdd ON pr.Person = pdd.Id //Selecting all Parents
)
SELECT pd.Name, s.Name Son, 'Son' Type FROM PersonData pd
JOIN Sons s on pd.Id = s.ParentId
UNION
SELECT pd.Name, gs.Name Son, 'GrandSon' Type FROM PersonData pd
JOIN Sons s on pd.Id = s.ParentId
JOIN Sons gs on s.Id = gs.ParentId

Answer 2

Try something like this (untested):
declare #person bigint = 123
;with cte as
(
select p.id, p.name, r.relativetype, r.parent, 0 decendantLevel
from person p
inner join relatives r
on p.id = r.person
where p.id = #person --select the ancestor who's tree we're interested in (if we don't want to include the person themselves change p.id to r.parent)
union all
select p.id, p.name, r.relativetype, r.parent, c.decendantLevel + 1
from person p
inner join relatives r
on p.id = r.person
inner join cte c
on c.id = r.parentid
)
select * from cte order by decendantLevel

Answer 3

Like mentioned recursive CTE is way to achieve this:
DECLARE #PersonToFind INT
SET #PersonToFind = 1
;WITH RCTE AS
(
SELECT Person, CAST('Child' AS NVARCHAR(MAX)) AS Relation
FROM PersonRelations
WHERE Father = #PersonToFind OR Mother = #PersonToFind
UNION ALL
SELECT pr.Person, 'Grand' + r.Relation
FROM PersonRelations pr
INNER JOIN RCTE r ON r.Person = pr.Mother OR r.Person = pr.Father
)
SELECT r.*, p.Name
FROM RCTE r
LEFT JOIN Person p ON r.Person = p.ID
SQLFiddle DEMO
(this is using mother and father columns before question was edited, so just change to Parent where there are Mother OR Father checks)

Answer 4

Thanks for all the answers, CTE was the way to go. I taked parts from every answer and ended with this
with Sons as (select P1.Person as PersonSon from Persons
join relatives as P1 on P1.Parent = Persons.Id
where Persons.Name = 'Mary')
select Id from Persons
join (
select P2.Person as PersonSon from Relatives as P2
join Sons on P2.Parent = Sons.PersonSon ) as P3 on Persons.Id = P3.PersonSon
union all select Sons.PersonSon from Sons