Group All Related Records in Many to Many Relationship, SQL graph connected components

Question

Hopefully I\'m missing a simple solution to this.

I have two tables. One contains a list of companies. The second contains a list of publishers. The mapping between

Answer 1

This is a recursive solution, using XML:

with a as ( -- recursive result, containing shorter subsets and duplicates
    select cast('' + company + '' as xml) as companies
          ,cast('
' + publisher + '
' as xml) as publishers
      from Table1

    union all

    select a.companies.query('for $c in distinct-values((for $i in /c return string($i),
                                                        sql:column("t.company")))
                          order by $c
                          return {$c}')
          ,a.publishers.query('for $p in distinct-values((for $i in /p return string($i),
                                                         sql:column("t.publisher")))
                          order by $p
                          return 
{$p}
')
    from a join Table1 t
      on (   a.companies.exist('/c[text() = sql:column("t.company")]') = 0 
          or a.publishers.exist('/p[text() = sql:column("t.publisher")]') = 0)
     and (   a.companies.exist('/c[text() = sql:column("t.company")]') = 1
          or a.publishers.exist('/p[text() = sql:column("t.publisher")]') = 1)
), b as ( -- remove the shorter versions from earlier steps of the recursion and the duplicates
    select distinct -- distinct cannot work on xml types, hence cast to nvarchar
           cast(companies as nvarchar) as companies
          ,cast(publishers as nvarchar) as publishers
          ,DENSE_RANK() over(order by cast(companies as nvarchar), cast(publishers as nvarchar)) as groupid
     from a
    where not exists (select 1 from a as s -- s is a proper subset of a
                       where (cast('' + cast(s.companies as varchar)
                                 + '' + cast(a.companies as varchar) + '' as xml)
                             ).value('if((count(/s/c) > count(/a/c))
                                         and (some $s in /s/c/text() satisfies
                                             (some $a in /a/c/text() satisfies $s = $a))
                                      ) then 1 else 0', 'int') = 1
                     )
      and not exists (select 1 from a as s -- s is a proper subset of a
                       where (cast('' + cast(s.publishers as nvarchar)
                                 + '' + cast(a.publishers as nvarchar) + '' as xml)
                             ).value('if((count(/s/p) > count(/a/p))
                                         and (some $s in /s/p/text() satisfies
                                             (some $a in /a/p/text() satisfies $s = $a))
                                      ) then 1 else 0', 'int') = 1
                     )
), c as (  -- cast back to xml
    select cast(companies as xml) as companies
          ,cast(publishers as xml) as publishers
          ,groupid
      from b
)
select Co.company.value('(./text())[1]', 'varchar') as company
      ,Pu.publisher.value('(./text())[1]', 'varchar') as publisher
      ,c.groupid
  from c
       cross apply companies.nodes('/c') as Co(company)
       cross apply publishers.nodes('/p') as Pu(publisher)
 where exists(select 1 from Table1 t -- restrict to only the combinations that exist in the source
               where t.company = Co.company.value('(./text())[1]', 'varchar')
                 and t.publisher = Pu.publisher.value('(./text())[1]', 'varchar')
             )

The set of companies and the set of publishers are kept in XML fields in the intermediate steps, and there is some casting between xml and nvarchar necessary due to some limitations of SQL Server (like not being able to group or use distinct on XML columns.