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

Here is my solution SQL Fiddle

The nature of the relationships require looping as I figure.

Here is the SQL:

--drop TABLE Table1

CREATE TABLE Table1
    ([row] int identity (1,1),GroupID INT NULL,[Company] varchar(2), [Publisher] varchar(2))
;

INSERT INTO Table1
    (Company, Publisher)
select
    left(newid(), 2), left(newid(), 2)

declare @i int = 1

while @i < 8
begin
    ;with cte(Company, Publisher) as (
        select
            left(newid(), 2), left(newid(), 2)
        from Table1
    )
    insert into Table1(Company, Publisher)
    select distinct c.Company, c.Publisher
    from cte as c
    where not exists (select * from Table1 as t where t.Company = c.Company and t.Publisher = c.Publisher)

    set @i = @i + 1
end;


CREATE NONCLUSTERED INDEX IX_Temp1 on Table1 (Company)
CREATE NONCLUSTERED INDEX IX_Temp2 on Table1 (Publisher)

declare @counter int=0
declare @row int=0
declare @lastnullcount int=0
declare @currentnullcount int=0

WHILE EXISTS (
  SELECT *
  FROM Table1
  where GroupID is null
  )
BEGIN
    SET @counter=@counter+1
    SET @lastnullcount =0

    SELECT TOP 1
        @row=[row]
    FROM Table1
    where GroupID is null
    order by [row] asc

    SELECT @currentnullcount=count(*) from table1 where groupid is null
    WHILE @lastnullcount <> @currentnullcount
    BEGIN
        SELECT @lastnullcount=count(*)
        from table1
        where groupid is null 

        UPDATE Table1
        SET GroupID=@counter
        WHERE [row]=@row

        UPDATE t2
        SET t2.GroupID=@counter
        FROM Table1 t1
        INNER JOIN Table1 t2 on t1.Company=t2.Company
        WHERE t1.GroupID=@counter
        AND t2.GroupID IS NULL

        UPDATE t2
        SET t2.GroupID=@counter
        FROM Table1 t1
        INNER JOIN Table1 t2 on t1.publisher=t2.publisher
        WHERE t1.GroupID=@counter
        AND t2.GroupID IS NULL

        SELECT @currentnullcount=count(*)
        from table1
        where groupid is null
    END
END

SELECT * FROM Table1

Edit: Added indexes as I would expect on the real table and be more in line with the other data sets Roman is using.