同じ列 SQL の 2 つの日付の DateDiff

テーブルをそれ自体に結合するだけです:

SELECT t1.OrderNo,DATEDIFF(day,t1.LoadedStartDate,t2.LoadedStartDate)
FROM UnnamedTableFromQuestion t1
       INNER JOIN
     UnnamedTableFromQuestion t2
       on
         t1.OrderNo = t2.OrderNo
WHERE t1.OpNo = 1 and
      t2.OpNo = 4