How to fit multiple equal references into table structure? - sql

Question

How to fit multiple equal references into table structure? How could I do that? For example: I have list of classmates:
1 Peter
2 Jack
3 John
4 Mary
5 Birgit
6 Stella
7 Janus
8 Margo
9 Fred
Now I want to define fellowships. In first place, let's limit that every kid may belong to one fellowship. So we could have 3 fellowships:
[Peter, Jack]
[John, Mary, Birgit]
[Stella, Janus, Margo, Fred]
All members are equal, so they all should reference to other members. Is there better ways to define such relations than just to have table of pairs? Like:
1 2
3 4
3 5
4 5
4 3
5 3
5 4
6 7
6 8
6 9
7 6
7 8
7 9
8 6
8 7
8 9
9 6
9 7
9 8
If using table of pairs, is it better to describe relation both way (like above), or is it enough to have link just from one way to another? What are the benefits of both ways?
Table of pairs does not constrain any member into just one fellowsip, but how would it possible?
I was looking for SQL table solution, but maybe there are better tools for handling such data-structures, so I added nosql-tag too. I am looking for right tools for such data, but I am eager to know, how to fit it in SQL tables too.

Answer 1

Yes, there is another way. If you have "fellowships", then you do not have pair-wise relationships. STart with a Fellowships table that has a FellowshipsId.
Then you would have a FellowshipsKids table. This is called a junction table, and it would have one row for each member of each fellowship. It would have rows like this:
FellowshipId KidId
1 1
1 2
2 3
2 4
2 5
. . .
What you have is an m-n relationship between fellowships and kids -- one fellowship can have multiple kids, one kids can be in multiple fellowships. A junction table is the standard way of represent this in a relational database.