apply recursive left join - recursion

Question

I'm using SQL Server 2012 and I have the following problem:
I have the this table (Category):
IDCategory| CategoryDesc | Father
1 | R1 | 0
2 | R1 - ST | 1
3 | R1 - CT | 1
4 | R1 - ST - SA | 2
5 | R1 - ST - CA 10 | 2
6 | R1 - ST - CA 20 | 2
7 | R1 - CT - CA | 3
8 | R1 - CT - SA | 3
9 | R2 | 0
10 | R2 ST | 9
.
.
until R9
And this one (CategoryDefinition):
IDCategory| First| Last
1 | 0 | 300
9 | 301 | 600
.
.
.
And I'm using the following query because I know there're only 3 levels:
SELECT
cat3.IDCategory,
cat.CategoryDesc AS title1,
cat2.CategoryDesc AS title2,
cat3.CategoryDesc AS title3,
catdef.First,
catdef.Last
FROM Category as cat
LEFT JOIN Category AS cat2 ON cat2.Father=cat.IDCategory
LEFT JOIN Category AS cat3 ON cat3.Father=cat2.IDCategory
INNER JOIN CategoryDefinition as catdef on cat.IDCategory = catdef.IDCategory
WHERE cat3.IDCategory = 7
Query result:
IDCategory| title1 | title2 |title3 |First|Last
7 | R1 | R1 - CT | R1 - CT - CA | 0 | 300
But how can I make this recursive? In the case that in the future could appear new levels (So I don't have to add a new left join for each new level that appears).
Thanks!

Answer 1

I can at least help with the recusive cte of an adjacency list and building a materialized path:
For this table:
create table category (IDCategory int primary key,CategoryDesc varchar(32),Father int)
insert into category values
(1,'R1',0)
,(2,'ST',1)
,(3,'CT',1)
,(4,'SA',3)
,(5,'SA 10',2)
,(6,'SA 20',2)
,(7,'CA',2)
,(8,'SA',2)
,(9,'R2',0)
,(10,'ST',9)
using a recursive cte:
;with cte as (
-- anchor elements: where Father = 0
select
IDCategory
, categoryDesc
, Father
, parentName = convert(varchar(32),null)
, path = convert(varchar(128),categoryDesc)
from category
where Father = 0
-- recursion begins here
union all
select
c.IDCategory
, c.categoryDesc
, c.Father
, parentName = p.categoryDesc
, path = convert(varchar(128),p.path+' - '+c.categoryDesc)
from category c
inner join cte as p on c.Father= p.IDCategory
)
-- we select all the results
select cte.*
from cte
order by idCategory
returns:
+------------+--------------+--------+------------+-----------------+
| IDCategory | categoryDesc | Father | parentName | path |
+------------+--------------+--------+------------+-----------------+
| 1 | R1 | 0 | NULL | R1 |
| 2 | ST | 1 | R1 | R1 - ST |
| 3 | CT | 1 | R1 | R1 - CT |
| 4 | SA | 3 | CT | R1 - CT - SA |
| 5 | SA 10 | 2 | ST | R1 - ST - SA 10 |
| 6 | SA 20 | 2 | ST | R1 - ST - SA 20 |
| 7 | CA | 2 | ST | R1 - ST - CA |
| 8 | SA | 2 | ST | R1 - ST - SA |
| 9 | R2 | 0 | NULL | R2 |
| 10 | ST | 9 | R2 | R2 - ST |
+------------+--------------+--------+------------+-----------------+
Adding the join to the anchor of the recursive cte:
;with cte as (
-- anchor elements: where Father = 0
select
c.IDCategory
, c.categoryDesc
, c.Father
, parentName = convert(varchar(32),null)
, path = convert(varchar(128),c.categoryDesc)
, cd.First
, cd.Last
from category c
inner join CategoryDefinition cd
on c.IdCategory=cd.IdCategory
where Father = 0
-- recursion begins here
union all
select
c.IDCategory
, c.categoryDesc
, c.Father
, parentName = p.categoryDesc
, path = convert(varchar(128),p.path+' - '+c.categoryDesc)
, p.First
, p.Last
from category c
inner join cte as p on c.Father= p.IDCategory
)
select cte.*
from cte
--where IdCategory = 7
order by idCategory
rextester demo: http://rextester.com/POSVP81190
returns:
+------------+--------------+--------+------------+-----------------+-------+------+
| IDCategory | categoryDesc | Father | parentName | path | First | Last |
+------------+--------------+--------+------------+-----------------+-------+------+
| 1 | R1 | 0 | NULL | R1 | 0 | 300 |
| 2 | ST | 1 | R1 | R1 - ST | 0 | 300 |
| 3 | CT | 1 | R1 | R1 - CT | 0 | 300 |
| 4 | SA | 3 | CT | R1 - CT - SA | 0 | 300 |
| 5 | SA 10 | 2 | ST | R1 - ST - SA 10 | 0 | 300 |
| 6 | SA 20 | 2 | ST | R1 - ST - SA 20 | 0 | 300 |
| 7 | CA | 2 | ST | R1 - ST - CA | 0 | 300 |
| 8 | SA | 2 | ST | R1 - ST - SA | 0 | 300 |
| 9 | R2 | 0 | NULL | R2 | 301 | 600 |
| 10 | ST | 9 | R2 | R2 - ST | 301 | 600 |
+------------+--------------+--------+------------+-----------------+-------+------+