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

You are trying to find all of the connected components of your graph, which can only be done iteratively. If you know the maximum width of any connected component (i.e. the maximum number of links you will have to take from one company/publisher to another), you could in principle do it something like this:

SELECT
    MIN(x2.groupID) AS groupID,
    x1.Company,
    x1.Publisher
FROM Table1 AS x1
    INNER JOIN (
        SELECT
            MIN(x2.Company) AS groupID,
            x1.Company,
            x1.Publisher
        FROM Table1 AS x1
            INNER JOIN Table1 AS x2
            ON x1.Publisher = x2.Publisher
        GROUP BY
            x1.Publisher,
            x1.Company
    ) AS x2
    ON x1.Company = x2.Company
GROUP BY
    x1.Publisher,
    x1.Company;

You have to keep nesting the subquery (alternating joins on Company and Publisher, and with the deepest subquery saying MIN(Company) rather than MIN(groupID)) to the maximum iteration depth.

I don't really recommend this, though; it would be cleaner to do this outside of SQL.

Disclaimer: I don't know anything about SQL Server 2012 (or any other version); it may have some kind of additional scripting ability to let you do this iteration dynamically.