Re: how to group by similarity ?

Andreas <maps(dot)on(at)gmx(dot)net> writes:

> How would I group the table so that it shows groups that have
> similarity () > x ?
>
> Lets say the table looks like this:
>
> id, txt
> 1, aa1
> 2, bb1
> 3, cc1
> 4, bb2
> 5, bb3
> 6, aa2
> ...
>
> How would a select look like that shows:
>
> id, txt, group_id
> 1, aa1, 1,
> 6, aa2, 1,
> 2, bb1, 2,
> 4, bb2, 2,
> 5, bb3, 2,
> 3, cc1, 3

I could only come up with this convoluted query:

WITH grp (t1, id, t2) AS (
SELECT t1.txt, t1.id, t2.txt
FROM tbl t1
LEFT JOIN tbl t2 ON t2.txt > t1.txt
WHERE t2.txt IS NULL OR similarity(t1.txt, t2.txt) > 0
)
SELECT t1, min(id)
FROM (
SELECT t1, id
FROM grp
UNION ALL
SELECT t2, id
FROM grp
WHERE t2 IS NOT NULL
) dummy
GROUP BY t1
ORDER BY t1