Need help in grouping records

Hi,

I'm trying to fight against double entries in tables.
I got as far as I can find similar records with trigram string matching.
If I do this with a table compared to itself I get something like this:

id_a, id_b
3,   5
3,   7
5,   3
5,   7
7,   3
7,   5
11,   13
13,   11

so the records with the IDs 3, 5, 7 and 11, 13 are similar enough to 
form a group.

How would I get a list of record-IDs with a group-ID like this

record_id, group_id
3,   1
5,   1
7,   1
11,   2
13,   2


Is there a way to get this by SQL ?