text: SELECT m.FirstName + ' ' + m.LastName AS Mechanic,
         AVG(DATEDIFF(DAY, j.IssueDate, j.FinishDate)) AS [Average Days]
    FROM Mechanics AS m
  JOIN Jobs j ON j.MechanicId = m.MechanicId
  GROUP BY m.MechanicId, m.FirstName + ' ' + m.LastName
  ORDER BY m.MechanicId