Question

I have a table that represents a series of matches between ids from another table as follows:

CREATE TABLE #matches (   asid1 int,   asid2 int )  insert into #matches values (1,2) insert into #matches values (1,3) insert into #matches values (3,1) insert into #matches values (3,4) insert into #matches values (7,6) insert into #matches values (5,7) insert into #matches values (8,1) insert into #matches values (1,8) insert into #matches values (8,9) insert into #matches values (8,3) insert into #matches values (10,11) insert into #matches values (12,10) 

and I want to find groups of matches that are linked directly or indirectly to one another.

The output would look like this:

group  asid 1      1 1      2 1      3 1      4 1      8 1      9 2      5 2      6 2      7 3      10 3      11 3      12 

if I were to add another row:

insert into #matches values (7,8) 

then this would mean that 2 of the groups above would be linked, so I would require output:

group  asid 1      1 1      2 1      3 1      4 1      5 1      6 1      7 1      8 1      9 2      10 2      11 2      12 

Any ideas?

Edit: Further research leads me to believe that a recursive common table expression should do the trick… if I figure out something elegant I’ll post it

Answer 1

It appears that a Disjoint-set is what you need to solve this. Here is a listing of a C# and C++ implementation.