Question

I’m trying to create a query that can fetch results in a many to many relationship database.
So far I got the following:
One table with songs, one table with tags and a ‘linking’ table as one song can have multiple tags and one tag can belong to multiple songs.

it looks like this:

Songs       Link        Tags
=======     =====       =========
Sid          Sid        Tid
Songname     Tid        Tagname

Now suppose you have 3 songs A B and C and 3 tags: X, Y and Z.
Song A has tag Y, song B has tag Z, and song C has tag X and Z.

I’ve managed to create a query to get a song by just one tag (e.g. Z gives B and C).
But how do i create a query that searches for songs when mutiple tags are enterred (e.g. typed into a (search) field).

I’ve searched and a few times the commands INTERSECT and INNER JOIN came up, but i havent been able to succesfully create a query.

Any help is appreciated!

Answer 1

This one will get all songs, that match any of the Tags, returning those which match all of them first:

SELECT s.Sid, s.Songname
FROM Songs s
JOIN Link l ON ( l.Sid = s.Sid )
JOIN Tags t ON ( t.Tid = s.Tid )
WHERE t.Tagname IN ( 'X', 'Y' )
GROUP BY s.Sid, s.Songname
ORDER BY COUNT(1) DESC

---

This one will only return those songs, that match all of the Tags:

SELECT s.Sid, s.Songname
FROM Songs s
JOIN Link l ON ( l.Sid = s.Sid )
JOIN Tags t ON ( t.Tid = s.Tid )
WHERE t.Tagname IN ( 'X', 'Y' )
GROUP BY s.Sid, s.Songname
HAVING COUNT(1) = 2 -- 'X' and 'Y'

If you generate this query, you will have to generate the count too (2 in my case).