sql query for getting the relation - sql

Question

Two tables are defined below. Names are arranged in a parent-child relationship. how to Show a nested (tree) list of names including [Id], [Name] and [Level], where [Level] indicates the nest level from the top (Root: Level = 0; First children of Root: Level = 1; etc…).
CREATE TABLE [Names]
(
[Id] INT PRIMARY KEY,
[Name] VARCHAR(100)
)
CREATE TABLE [Relationships]
(
[Parent] [int] REFERENCES [Names]([Id]),
[Child] [int] REFERENCES [Names]([Id])
)
INSERT [NAMES] VALUES (1,'FRANK')
INSERT [NAMES] VALUES (2,'JO')
INSERT [NAMES] VALUES (3,'MARY')
INSERT [NAMES] VALUES (4,'PETER')
INSERT [NAMES] VALUES (5,'MAY')
INSERT [RELATIONSHIPS] VALUES (1,0)
INSERT [RELATIONSHIPS] VALUES (2,1)
INSERT [RELATIONSHIPS] VALUES (3,2)
INSERT [RELATIONSHIPS] VALUES (4,1)
INSERT [RELATIONSHIPS] VALUES (5,2)
I am using ms sql server 2008

Answer 1

I think this is sweet and simple way
SELECT child AS ID , N.Name , ISNULL(R.Parent, 0) AS Lavel
FROM Relationships R ,NAMES N
WHERE R.Child = N.Id ORDER BY parent,child
ID Name Level
1 FRANK 0
2 JO 1
4 PETER 1
3 MARY 2
5 MAY 2

Answer 2

common table expressions allow you to do recursive calls for things like this. Search for that. It will go something like this:
with cte as (
select *, 1 as lvl
from relationships as a
join names as b ...
union
select *, lvl + 1
from ....
)
select * from cte;
I may not have it exactly right, but searching for cte recursion will help.

Answer 3

Use Recursive CTE to do this.
;WITH cte
AS (SELECT NAME,
Parent,
Child,
0 AS level
FROM [Names] N
JOIN Relationships r
ON r.Parent = n.Id
WHERE Child IS NULL
UNION ALL
SELECT b.NAME,
b.Parent,
b.Child,
level + 1
FROM cte a
JOIN (SELECT NAME,
Parent,
Child
FROM [Names] N
JOIN Relationships r
ON r.Parent = n.Id) b
ON a.Parent = b.Child)
SELECT * FROM cte
Note : In Relationship table first row (ie) INSERT [RELATIONSHIPS] VALUES (1,0) you cannot insert 0 in child column since Names table does not have such entry.
If it is the root then then you can use NULL instead of 0 like INSERT [RELATIONSHIPS] VALUES (1,null)

Answer 4

CREATE TABLE [Names]
(
[Id] INT PRIMARY KEY,
[Name] VARCHAR(100)
)
CREATE TABLE [Relationships]
(
[Child] [int] REFERENCES [Names]([Id]),
[Parent] [int] REFERENCES [Names]([Id])
)
INSERT [NAMES] VALUES (1,'FRANK')
INSERT [NAMES] VALUES (2,'JO')
INSERT [NAMES] VALUES (3,'MARY')
INSERT [NAMES] VALUES (4,'PETER')
INSERT [NAMES] VALUES (5,'MAY')
INSERT [RELATIONSHIPS] VALUES (1,Null)
INSERT [RELATIONSHIPS] VALUES (2,1)
INSERT [RELATIONSHIPS] VALUES (3,2)
INSERT [RELATIONSHIPS] VALUES (4,1)
INSERT [RELATIONSHIPS] VALUES (5,4)
--first have a look at INSERT [RELATIONSHIPS] VALUES (1,0), you are
--saying 0 is the child of 1. I think you need to swap the column
--names? - this solution assumes you meant parent to be child
--and visa-versa - i.e. I swapped them above
--second, do you need the relationships table? cant you just have a
--reports_to column in the names table?
--third, you cant have a value of 0 in either column of your relationships
--table because of the FK constraint to names - no name exists
--with id = 0, insert NULL instead
--fourth, I changed May's manager so that it was clear that lvl & manager werent related
;with
cte as
(select id, name, isnull(parent,0) as manager
from Names n
left join Relationships r
on r.child = n.id),
r_cte as
(select 0 as lvl, id, name, manager
from cte
where manager = 0
union all
select r.lvl + 1, c.id, c.Name, c.manager
from cte c
inner join r_cte r
on c.manager = r.id
)
select * from r_cte