SELECT * FROM
(
SELECT DISTINCT TOP 15 G.Lastname as Lastname, 
G.SubDirectory as SubDirectory, G.Firstname as Firstname, 
G.Gallery as Gallery, G.Custnumber as Custnumber, 
I.ImageNumber as Imagenumber, I.ImagePosition as ImagePosition,
 I.RecordNo, I.ImageSizeList, I.GeneralRandomNo as GeneralRandomNo,
 p.ImgQty as ImageQTy, P.Subdirectory as Portfolio, 
P.DateTime as DateTime, p.ExhibitionOpened, P.RandomNo, 
P.AutoID as AutoID, I.PortfolioName, newid() as RandID,
ROW_NUMBER() OVER (PARTITION BY G.Lastname, G.FirstName ORDER BY NEWID()) AS RN
FROM ArtistSetup G INNER JOIN
ArtistPortfolios P ON G.Custnumber = P.Custnumber INNER JOIN
ArtistIndividualWorks I ON P.SubDirectory = I.PortfolioName AND I.Custnumber = G.Custnumber
WHERE P.ImgQty>0 AND G.Gallery='PhotoBistro' and I.ImagePosition=1 and P.ShowcaseOK=1
) R
where RN = 1
Order by ExhibitionOpened desc