date difference in number of days sql server
DECLARE
@start_dt DATETIME2= '2019-12-31 23:59:59.9999999',
@end_dt DATETIME2= '2020-01-01 00:00:00.0000000';
SELECT
DATEDIFF(year, @start_dt, @end_dt) diff_in_year,
DATEDIFF(quarter, @start_dt, @end_dt) diff_in_quarter,
DATEDIFF(month, @start_dt, @end_dt) diff_in_month,
DATEDIFF(dayofyear, @start_dt, @end_dt) diff_in_dayofyear,
DATEDIFF(day, @start_dt, @end_dt) diff_in_day,
DATEDIFF(week, @start_dt, @end_dt) diff_in_week,
DATEDIFF(hour, @start_dt, @end_dt) diff_in_hour,
DATEDIFF(minute, @start_dt, @end_dt) diff_in_minute,
DATEDIFF(second, @start_dt, @end_dt) diff_in_second,
DATEDIFF(millisecond, @start_dt, @end_dt) diff_in_millisecond;