text: SELECT m.ModelId, m.Name ,
  	 CAST(AVG(DATEDIFF(DAY, j.IssueDate, j. FinishDate)) AS varchar(50)) + ' ' + 'days'  AS [Average Service Time]
   FROM Models AS m
  JOIN Jobs AS j ON m.ModelId = j.ModelId
  WHERE j.FinishDate IS NOT NULL
  GROUP BY m.ModelId, m.Name
  ORDER BY AVG(DATEDIFF(DAY, j.IssueDate, j. FinishDate))