Implementace sql serveru s více rodiči (nebo digrafem) 2005

Nakonec jsem přišel s následujícím řešením. Zjistil jsem, že je to způsob, jak podporuje vícekořenové stromy a také cyklické digrafy.

create table #ObjectRelations
(
    Id varchar(20),
    NextId varchar(20)
)

/* Cycle */
/*
insert into #ObjectRelations values ('A', 'B')
insert into #ObjectRelations values ('B', 'C') 
insert into #ObjectRelations values ('C', 'A')
*/

/* Multi root */

insert into #ObjectRelations values ('G', 'B')
insert into #ObjectRelations values ('A', 'B') 
insert into #ObjectRelations values ('B', 'C')
insert into #ObjectRelations values ('B', 'X')
insert into #ObjectRelations values ('C', 'E') 
insert into #ObjectRelations values ('C', 'D') 
insert into #ObjectRelations values ('E', 'F') 
insert into #ObjectRelations values ('D', 'F') 


declare @startIds table
(
    Id varchar(20) primary key
)

;WITH 
    Ids (Id) AS
    (
        SELECT  Id
        FROM    #ObjectRelations
    ),
    NextIds (Id) AS
    (
        SELECT  NextId
        FROM    #ObjectRelations
    )
INSERT INTO @startIds
/* This select will not return anything since there are not objects without predecessor, because it's a cyclic of course */
SELECT DISTINCT
    Ids.Id
FROM
    Ids
LEFT JOIN
    NextIds on Ids.Id = NextIds.Id
WHERE
    NextIds.Id IS NULL
UNION
/* So let's just pick anyone. (the way I will be getting the starting object for a cyclic doesn't matter for the regarding problem)*/
SELECT TOP 1 Id FROM Ids

;WITH Objects (Id, NextId, [Level], Way) AS
( -- This is the 'Anchor' or starting point of the recursive query
  SELECT rel.Id,
         rel.NextId,
         1,
         CAST(rel.Id as VARCHAR(MAX))
    FROM #ObjectRelations rel
   WHERE rel.Id IN (SELECT Id FROM @startIds)

   UNION ALL -- This is the recursive portion of the query

  SELECT rel.Id,
         rel.NextId,
         [Level] + 1,
         RecObjects.Way + ', ' + rel.Id
    FROM #ObjectRelations rel
   INNER JOIN Objects RecObjects -- Note the reference to CTE table name (Recursive Join)
      ON rel.Id = RecObjects.NextId
   WHERE RecObjects.Way NOT LIKE '%' + rel.Id + '%'

)
SELECT  DISTINCT 
        Id,
        NextId,
        [Level]
FROM    Objects
ORDER BY [Level]

drop table #ObjectRelations

Může být pro někoho užitečné. To je pro mě =Díky