Something like this?

;WITH Ordered AS(

SELECTDISTINCT

CASE WHEN l.Col1 <= l.Col2 THEN l.Col1 ELSE l.Col2 END AS Col1,

CASE WHEN l.Col1 <= l.Col2 THEN l.Col2 ELSE l.Col1 END AS Col2

FROM Links l

),

rCTE AS(

SELECT Col1 AS Parent,

Col1,

Col2

FROM Ordered l

UNION ALL

SELECT c.Parent,

l.Col1,

l.Col2

FROM Ordered l

JOIN rCTE c ON l.Col1 = c.Col2

),

Row_Values AS(

SELECT Parent Col1,

Col2,

ROW_NUMBER() OVER( PARTITION BY Col2 ORDER BY Parent) rn

FROM rCTE

)

SELECT Col1, Col2

FROM Row_Values

WHERE rn = 1

ORDER BY Col1, Col2

Unless someone finds a more effective way to do it.