SQL Datetime as Duration String (days – hours – minutes – seconds)

DECLARE 
@start DATETIME = '2018-01-03 20:10:36.000', 
@end DATETIME = '2018-01-03 22:10:37:000' 

select IIF(convert(varchar(10), (DATEDIFF(SECOND, @start, @end ) / 86400)) = '0', '', convert(varchar(10), (DATEDIFF(SECOND, @start, @end )/86400)) + ' days ') 
+ IIF(convert(varchar(10), ((DATEDIFF(SECOND, @start, @end ) % 86400) / 3600)) = '0', '', convert(varchar(10), ((DATEDIFF(SECOND, @start, @end )%86400)/3600)) + ' hours ') 
+ IIF(convert(varchar(10), (((DATEDIFF(SECOND, @start, @end ) % 86400) % 3600) / 60)) = '0', '', convert(varchar(10), (((DATEDIFF(SECOND, @start, @end )%86400)%3600)/60)) + ' minutes ')
+ IIF(convert(varchar(10), (((DATEDIFF(SECOND, @start, @end ) % 86400) % 3600) % 60)) ='0', '', convert(varchar(10), (((DATEDIFF(SECOND, @start, @end )%86400)%3600)%60)) + ' seconds') as 'Duration'