in a table column row by row subtraction to find the value in sql server : id	patient_date			
1	10/5/2017			
2	6/6/2017			
3	6/10/2017			
4	8/7/2017			
5	9/19/2017			
				
output:-				
id	 patient_date	   days		
1	10/5/2017	     (6/6/2017-10/5/2017)		
2	6/6/2017	     (6/10/2017-6/6/2017)		
3	6/10/2017	     (8/7/2017-6/10/2017)		
4	8/7/2017	     (9/19/2017-8/7/2017)		
5	9/19/2017			
   