Question

I have a table that shows the relationships between people a bit like this.

id  linked_id
1   2
1   3
3   4
4   1

There is no apparent order to the table or the relationships.

I’m trying to find a way to list all the ids that have any kind of link to a given id. So for examples from the table above:

id = 1 would return 1, 2, 3 and 4.
id = 2 would also return 1, 2, 3 and 4

It’s an oracle database, and the query would have to be in plain SQL. Thanks for your help, this has been driving me nuts.

Answer 1

You could use something like this:

SELECT linked_id
  FROM DATA
 START WITH ID = :1
CONNECT BY NOCYCLE PRIOR ID = linked_id
        OR ID = PRIOR linked_id
UNION
SELECT ID
  FROM DATA
 START WITH linked_id = :1
CONNECT BY NOCYCLE PRIOR ID = linked_id
        OR ID = PRIOR linked_id
UNION
SELECT :1 FROM dual