vis de øverste 3 poster i et komma adskilt i én kolonne

Jeg går ud fra, at "top tre" er de tre mest hyppigt forekommende elementer i kolonnen Ekspertise, men dette kan ændres, hvis det ikke er det, du mente.

WITH T1 AS (
    SELECT TOP(3) Expertise, COUNT(*) AS cnt
    FROM Expertise
    GROUP BY Expertise
    ORDER BY cnt DESC
), T2 AS (
   SELECT ROW_NUMBER() OVER (ORDER BY cnt DESC) AS rn, Expertise
   FROM T1
)
SELECT (SELECT Expertise FROM T2 WHERE rn = 1) + ',' + 
       (SELECT Expertise FROM T2 WHERE rn = 2) + ',' +
       (SELECT Expertise FROM T2 WHERE rn = 3)

Resultat:

dfdf,.NEt,fgfg