CREATE TABLE T ( [f1] VarCHAR(100), [f2] VarCHAR(100))
go
INSERT INTO T   VALUES ('a','abc')
INSERT INTO T   VALUES ('a','b')
INSERT INTO T   VALUES ('b','XX')
go

SELECT 
  F1,
  NameValues=STUFF(
(SELECT ','+F2 FROM T 
  WHERE F1=Results.F1 
  FOR XML PATH('')) 
  ,1,1,'')  

FROM T Results
GROUP BY F1