how to get the date diff on once field in sql server

1SELECT t1.OrderNo,DATEDIFF(day,t1.LoadedStartDate,t2.LoadedStartDate)
2FROM UnnamedTableFromQuestion t1
3       INNER JOIN
4     UnnamedTableFromQuestion t2
5       on
6         t1.OrderNo = t2.OrderNo
7WHERE t1.OpNo = 1 and
8      t2.OpNo = 4
9      
10////////////////////////////////////////////////////////////////
11
12select cur.unique_id_field, cur.seq_no, cur.date_created ,
13
14  datediff(second, prv.date_created, cur.date_created) as diff_in_seconds
15
16from yourtable as cur
17
18  join yourtable as prv
19
20    on cur.seq_no = prv.seq_no + 1;