;with Users (UserID,UserName,GroupID)
AS
(SELECT 1 ,'Joe',3 UNION ALL
SELECT 2 ,'Dave',5 UNION ALL
SELECT 3 ,'Geoff', 2 UNION ALL
SELECT 4 ,'Gordon', 1 UNION ALL
SELECT 5 ,'Jane', 4 )
,Groups (GroupID,GroupName)
AS
(SELECT 1,'Group1' UNION ALL
SELECT 2,'Group2' UNION ALL
SELECT...