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

Bit late to the challenge, and since SQLFiddle seems to be down ATM I'll have to guess your data-structures. Nevertheless, it seemed like a fun challenge (and it was =) so here's what I made from it :

Setup:

IF OBJECT_ID('t_link') IS NOT NULL DROP TABLE t_link
IF OBJECT_ID('t_company') IS NOT NULL DROP TABLE t_company
IF OBJECT_ID('t_publisher') IS NOT NULL DROP TABLE t_publisher
IF OBJECT_ID('tempdb..#link_A') IS NOT NULL DROP TABLE #link_A
IF OBJECT_ID('tempdb..#link_B') IS NOT NULL DROP TABLE #link_B
GO

CREATE TABLE t_company ( company_id     int IDENTITY(1, 1) NOT NULL PRIMARY KEY,
                         company_name   varchar(100) NOT NULL)

GO 

CREATE TABLE t_publisher (publisher_id     int IDENTITY(1, 1) NOT NULL PRIMARY KEY,
                          publisher_name   varchar(100) NOT NULL)

CREATE TABLE t_link (company_id int NOT NULL FOREIGN KEY (company_id) REFERENCES t_company (company_id),
                     publisher_id int NOT NULL FOREIGN KEY (publisher_id) REFERENCES t_publisher (publisher_id),
                                PRIMARY KEY (company_id, publisher_id),
                     group_id int NULL
                             )
GO

-- example content


-- ROW   GROUPID     Company     Publisher
--1     1           A           Y
--2     1           A           X
--3     1           B           Y
--4     1           B           Z
--5     2           C           W
--6     2           C           P
--7     2           D           W


INSERT t_company (company_name) VALUES ('A'), ('B'), ('C'), ('D')
INSERT t_publisher (publisher_name) VALUES ('X'), ('Y'), ('Z'), ('W'), ('P')

INSERT t_link (company_id, publisher_id)
SELECT company_id, publisher_id
  FROM t_company, t_publisher
 WHERE (company_name = 'A' AND publisher_name = 'Y')
    OR (company_name = 'A' AND publisher_name = 'X')
    OR (company_name = 'B' AND publisher_name = 'Y')
    OR (company_name = 'B' AND publisher_name = 'Z')
    OR (company_name = 'C' AND publisher_name = 'W')
    OR (company_name = 'C' AND publisher_name = 'P')
    OR (company_name = 'D' AND publisher_name = 'W')




GO

/*
-- volume testing

TRUNCATE TABLE t_link
DELETE t_company
DELETE t_publisher


DECLARE @company_count   int = 1000,
        @publisher_count int = 450,
        @links_count     int = 800


INSERT t_company (company_name)
SELECT company_name    = Convert(varchar(100), NewID())
  FROM master.dbo.fn_int_list(1, @company_count) 

UPDATE STATISTICS t_company

INSERT t_publisher (publisher_name)
SELECT publisher_name  = Convert(varchar(100), NewID())
  FROM master.dbo.fn_int_list(1, @publisher_count) 

UPDATE STATISTICS t_publisher

-- Random links between the companies & publishers

DECLARE @count int
SELECT @count = 0

WHILE @count < @links_count
    BEGIN

        SELECT TOP 30 PERCENT row_id = IDENTITY(int, 1, 1), company_id = company_id + 0
          INTO #link_A
          FROM t_company
         ORDER BY NewID()

        SELECT TOP 30 PERCENT row_id = IDENTITY(int, 1, 1), publisher_id = publisher_id + 0
          INTO #link_B
          FROM t_publisher
         ORDER BY NewID()

        INSERT TOP (@links_count - @count) t_link (company_id, publisher_id)
        SELECT A.company_id,
               B.publisher_id
          FROM #link_A A
          JOIN #link_B B
            ON A.row_id = B.row_id
         WHERE NOT EXISTS ( SELECT *
                              FROM t_link old
                             WHERE old.company_id   = A.company_id
                               AND old.publisher_id = B.publisher_id)

        SELECT @count = @count + @@ROWCOUNT

        DROP TABLE #link_A
        DROP TABLE #link_B    
    END

*/

Actual grouping:

IF OBJECT_ID('tempdb..#links') IS NOT NULL DROP TABLE #links
GO

-- apply grouping

-- init
SELECT row_id = IDENTITY(int, 1, 1), 
       company_id,
       publisher_id,
       group_id = 0
  INTO #links
  FROM t_link

-- don't see an index that would be actually helpful here right-away, using row_id to avoid HEAP
CREATE CLUSTERED INDEX idx0 ON #links (row_id)
--CREATE INDEX idx1 ON #links (company_id)   
--CREATE INDEX idx2 ON #links (publisher_id)

UPDATE #links
   SET group_id = row_id


-- start grouping
WHILE @@ROWCOUNT > 0
    BEGIN  
        UPDATE #links
           SET group_id = new_group_id
          FROM #links upd
          CROSS APPLY (SELECT new_group_id = Min(group_id)
                         FROM #links new
                        WHERE new.company_id   = upd.company_id
                           OR new.publisher_id = upd.publisher_id 
                                     ) x
        WHERE upd.group_id > new_group_id

        -- select * from #links
    END


-- remove 'holes'
UPDATE #links
   SET group_id = (SELECT COUNT(DISTINCT o.group_id) 
                          FROM #links o
                         WHERE o.group_id <= upd.group_id)
  FROM #links upd

GO

UPDATE t_link
   SET group_id = new.group_id
  FROM t_link upd
  LEFT OUTER JOIN #links new
               ON new.company_id = upd.company_id
              AND new.publisher_id = upd.publisher_id

GO    
SELECT row = ROW_NUMBER() OVER (ORDER BY group_id, company_name, publisher_name),
       l.group_id,
       c.company_name, -- c.company_id,
       p.publisher_name -- , p.publisher_id
 from t_link l
 JOIN t_company c
   ON l.company_id = c.company_id
 JOIN t_publisher p 
   ON p.publisher_id = l.publisher_id
 ORDER BY 1

At first sight this approach hasn't been tried yet by anyone else, interesting to see how this can be done in a variety of ways... (preferred not to read them upfront as it would spoil the puzzle =)

Results look as expected (as far as I understand the requirements and the example) and performance isn't too shabby either although there is no real indication on the amount of records this should work on; not sure how it would scale but don't expect too many problems either...