date difference in number of days sql server

1DECLARE 
2    @start_dt DATETIME2= '2019-12-31 23:59:59.9999999', 
3    @end_dt DATETIME2= '2020-01-01 00:00:00.0000000';
4
5SELECT 
6    DATEDIFF(year, @start_dt, @end_dt) diff_in_year, 
7    DATEDIFF(quarter, @start_dt, @end_dt) diff_in_quarter, 
8    DATEDIFF(month, @start_dt, @end_dt) diff_in_month, 
9    DATEDIFF(dayofyear, @start_dt, @end_dt) diff_in_dayofyear, 
10    DATEDIFF(day, @start_dt, @end_dt) diff_in_day, 
11    DATEDIFF(week, @start_dt, @end_dt) diff_in_week, 
12    DATEDIFF(hour, @start_dt, @end_dt) diff_in_hour, 
13    DATEDIFF(minute, @start_dt, @end_dt) diff_in_minute, 
14    DATEDIFF(second, @start_dt, @end_dt) diff_in_second, 
15    DATEDIFF(millisecond, @start_dt, @end_dt) diff_in_millisecond;

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;