Number of days patient was on ventilator

Try this,

declare @temp table (patent_id int, visit_id int, [name of PR] nvarchar(100),ventilator_StartDate datetime, ventilator_StopDate datetime)
insert into @temp values(1,100,'Adult Ventilator',getdate()-10,getdate()-8)
insert into @temp values(1,100,'Adult Ventilator',getdate()-8,getdate()-8)
insert into @temp values(3,100,'Adult Ventilator','02/05/2013','02/11/2013')
insert into @temp values(3,100,'Adult Ventilator','02/11/2013','02/11/2013')
insert into @temp values(4,100,'Adult Ventilator','01/18/2013','01/20/2013')
insert into @temp values(4,100,'Adult Ventilator','01/20/2013','01/23/2013')
------------------------
select patent_id, visit_id, [name of PR],datediff(d,min(ventilator_StartDate), max(ventilator_StopDate))+1 as Days
from @temp
group by patent_id, visit_id, [name of PR]

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Regards, RSingh