Question

I’ve a table with fields id_osztaly, id_csoportositas and name (and some other fields but there aren’t important).

I want create a query with the follow result: I want combine the name fields. I can’t explain so I show an example:
the datas in the table (id_osztaly, id_csoportositas and name order):

1,1,Group1A
1,1,Group1B
1,2,Group2A
1,2,Group2B

I want the follow combine from name:

Group1A-Group2A
Group1A-Group2B
Group1B-Group2A
Group1B-Group2B

(similar the permutation). I can do this with a JOIN, it’s ok. But when I three different value of id_csoportositas:

1,1,Group1A
1,1,Group1B
1,2,Group2A
1,2,Group2B
1,3,Group3A
1,3,Group3B
1,3,Group3C

I want:

Group1A-Group2A-Group3A
Group1A-Group2A-Group3B
Group1A-Group2A-Group3C
Group1A-Group2B-Group3A
Group1A-Group2B-Group3B
Group1A-Group2B-Group3C
Group1B-Group2A-Group3A
Group1B-Group2A-Group3B
Group1B-Group2A-Group3C
Group1B-Group2B-Group3A
Group1B-Group2B-Group3B
Group1B-Group2B-Group3C

Yes, it’s double join. But I don’t know how many different id_csoportositas exist in table. First blick I think I need same number of JOIN as the number of different id_csoportositas.

Is there any trick in (my)sql to do this or should I do it in PHP with a for-cycle?

EDIT maybe I wasn’t clear. I know how can I JOIN same table two times or three times. If I’ve two different id_csoportositas I need only one JOIN. If I’ve three different id_csoportositas I need two JOIN – I can do this too. But I don’t know how many different id_csoportositas exist so I don’t know how many JOIN will need. The number of JOINs depends on number of different id_csoportositas and I don’t know the number of id_csoportositas without a query.

And I want to group by id_osztaly and different id_osztaly has different id_csoportositas.

I hope it’s clear now.

Answer 1

Won’t something like this work:

SELECT * FROM
(
    (SELECT * FROM table WHERE something = 1) a,
    (SELECT * FROM table WHERE something = 2) b,
    (SELECT * FROM table WHERE something = 3) c
)

You just select like this and it would provide all possible variations of the joins 🙂