SELECT SG.Id 
      ,SG.GroupName  
      ,HostNames = STUFF((SELECT ‘,‘ + SH.[HostName]
          FROM SaltHost SH
          WHERE SG.Id = SH.HostGroupId
          FOR XML PATH(‘‘), TYPE).value(‘.‘, ‘NVARCHAR(MAX)‘), 1, 1, ‘‘)
FROM [SaltGroup] SG
ORDER BY SG.Id