Matching sets in SQL when cross-referencing

event target to filter down a selection like this:

var circleMatch = svg.selectAll(".highcircles")
    .filter(function(d) {
        return d.key === targetDatum.key;  // 'key' is some datum-unique property
    });

with relations 
--Get all single relationships between vendors.
as (
    select t1.vendorId firstId,
        t2.vendorId secondId
    from VendorMaster  t1
    inner join VendorMaster  t2 on t1.vendorId < t2.vendorId and(
            t1.Phone = t2.Phone
            or t1.address = t2.address
            or t1.Fax = t2.Fax
            )
    ),
recurseLinks
--Recurse the relationships
as (
    select r.*, CAST(',' + CAST(r.firstId AS VARCHAR) + ',' AS VARCHAR) tree
    from relations r

    union all

    select r.firstId,
        l.secondId,
        cast(r.Tree + CAST(l.secondId AS varchar) + ',' as varchar)
    from relations l
    inner join recurseLinks r on r.secondId = l.firstId and r.tree not like '%' + cast(l.secondId as varchar) + ',%'

    union all

    select r.firstId,
        l.firstId,
        cast(r.Tree + CAST(l.firstId AS varchar) + ',' as varchar)
    from relations l
    inner join recurseLinks r on r.secondId = l.secondId and r.tree not like '%' + cast(l.firstId as varchar) + ',%'
    ),
removeInvalid
--Removed invalid relationships.
as (
    select l1.firstId, l1.secondId
    from recurseLinks l1
    where l1.firstId < l1.secondId
    ),
removeIntermediate
--Removed intermediate relationships.
as (
    select distinct l1.*
    from removeInvalid l1
    left join removeInvalid l2 on l2.secondId = l1.firstId
    where l2.firstId is null
    )
select result.secondId,
    dense_rank() over(order by result.firstId) SetId
from (
    select firstId,
        secondId
    from removeIntermediate 

    union all

    select distinct firstId,
        firstId
    from removeIntermediate 
    ) result;

CREATE TABLE #t1 (IDChild Int, IDParent Int);
CREATE TABLE #t2 (RandoID NVARCHAR(10) , IDChild Int);
CREATE TABLE #RandoName (RandoID NVARCHAR(10), RandoName VARCHAR(50));

INSERT INTO #t1 VALUES (321, NULL), (123,321),(124,123),(116,124)
INSERT INTO #t2 VALUES ('asdf', 123)
INSERT INTO #RandoName VALUES ('asdf', 'something')

SELECT ROW_NUMBER() OVER (ORDER BY (SELECT 100)) [RowNum], a.IDChild a, a.IDParent b, b.IDChild c INTO #t3 FROM #t1 a
LEFT OUTER JOIN #t1 b ON b.IDParent = a.IDChild

DECLARE @rownum INT;
DECLARE cbcursor CURSOR for Select RowNum FROM #t3;
OPEN cbcursor;
Fetch Next from cbcursor into @rownum
WHILE @@FETCH_STATUS = 0
BEGIN
       UPDATE #t3
       SET c = (SELECT b from #t3 where RowNum = @rownum-1)
       WHERE RowNum = @rownum
Fetch Next from cbcursor into @rownum;
END;
Close cbcursor;
Deallocate cbcursor;

SELECT a,b,t2.RandoID, r.RandoName FROM #t3
LEFT OUTER JOIN #t2 t2 on t2.IDChild = #t3.c OR t2.IDChild = #t3.b OR t2.IDChild = #t3.a
LEFT OUTER JOIN #RandoName r on t2.RandoID = r.RandoID

SELECT CONCAT(c.course_id,': ',c.title) AS Course, 
       CONCAT(p.prereq_id,': ',pc.title) AS Prerequisite

FROM uni_course AS c   
INNER JOIN uni_prereq AS p ON c.course_id = p.course_id
INNER JOIN uni_course AS pc ON p.prereq_id = pc.course_id;