Find all parent and child with a relationship table - sql

Question

I have inherited two tables:
Table 1: Loc
LocID Field1 Field2
---------------------------
1 AAA BBB
2 CCC DDD
3 EEE FFF
4 GGG HHH
5 III JJJ
6 KKK LLL
7 MMM NNN
8 OOO PPP
9 QQQ RRR
10 SSS TTT
11 UUU VVV
Table 2: LocRel
LocID_A LocID_B
-----------------------
1 2
1 3
2 4
2 5
3 6
3 7
5 11
8 9
8 10
So, the LocRel table basically is used to specified the relationships between the various records in the Loc table.
I am struggling with writing a sql statement that will list all the relationships like so:
LocID Level LocIDH_Ancestry Field1 Field2
---------------------------------------------------
1 1 NULL AAA BBB
2 2 1 CCC DDD
3 2 1 EEE FFF
4 3 1,2 GGG HHH
5 3 1,2 III JJJ
6 3 1,3 KKK LLL
7 3 1,3 MMM NNN
8 1 NULL OOO PPP
9 2 8 QQQ RRR
10 2 8 SSS TTT
11 4 1,2,5 UUU VVV
I am not good at all in queries involving relationships, and would really appreciate some help on how the above can be achieved.
Thank you to all!

Answer 1

This answer may be SQL Server specific. I'm not an expert in SQL, so I don't know how much of this is standard and/or adopted in other dbms.
You can implement the kind of queries you mentioned, using recursive queries. Here is a intro to the subject that provides a good starting point.
For your specific query, something like this should do the work.
WITH MyCTE AS
(
SELECT
LocID, 1 as Level,
NULL as LocIDH_Ancestry,
Field1, Field2
FROM
Table1
WHERE
LocID NOT IN (SELECT LocID_B FROM Table2)
UNION ALL
SELECT
t1.LocID,
c.Level + 1 as Level,
t2.LocID_A as LocIDH_Ancestry,
t1.Field1, t1.Field2
FROM
Table1 t1
INNER JOIN
Table2 t2 ON t1.LocID = t2.LocID_A
INNER JOIN
MyCTE c ON t2.LocID_B = c.LocID
)
SELECT *
FROM MyCTE
Hope that helps.