set nocount on
create table #scratch_table (identity_key int, sample_datetime datetime, stack_ID varchar(16))
insert #scratch_table
select 1, '2001-06-02 00:00:00.000', NULL union all
select 7, '2006-01-02 10:50:22.000', 'H505-2006-12-001' union all
select 8, '2006-01-02 10:50:25.000', 'H505-2006-12-003' union all
select 9, '2006-01-02 10:50:30.000', 'H505-2006-12-004' union all
select 10, '2006-03-02 10:50:30.000', 'H505-2006-12-004' union all
select 11, '2006-03-03 10:50:30.000', 'H505-2006-12-004' union all
select 16, '2006-03-04 13:21:58.000', 'H505-2006-12-001' union all
select 17, '2006-03-04 15:33:12.000', 'H505-2006-12-003' union all
select 18, '2006-03-04 15:34:15.000', 'H505-2006-12-003' union all
select 21, '2006-03-05 10:45:25.000', 'H505-2006-12-005' union all
select 38, '2006-03-06 11:05:25.000', 'H505-2006-12-007' union all
select 41, '2006-03-16 13:27:21.000', 'H505-2006-12-004' union all
select 42, '2006-03-16 13:27:21.500', 'H505-2006-12-004' union all
select 43, '2006-03-16 13:27:21.100', 'H505-2006-12-004'


select	interval_milliseconds = abs(datediff(millisecond, last, most_Recent))
	,[last]
	,most_recent
from	(
	select	sample_datetime [last]
		,most_recent = (select top 1 sample_datetime 
				from #scratch_table 
				where stack_id = a.stack_id 
				order by sample_datetime desc) 
	from	#Scratch_table a
	where	identity_key = (select max(identity_key) identity_key from #scratch_table)
	) a


drop table #scratch_table


output:

interval_milliseconds last                                                   most_recent                                            
--------------------- ------------------------------------------------------ ------------------------
400                   2006-03-16 13:27:21.100                                2006-03-16 13:27:21.500

select datediff(ms, b.sample_datetime, max(a.sample_datetime)) as interval_milliseconds
    , b.sample_datetime as last
    , max(a.sample_datetime) as most_recent
from #scratch_table a
    inner join
        (select stack_id, sample_datetime from #scratch_table
        where identity_key = (select max(identity_key) from #scratch_table)) b
    on a.stack_id = b.stack_id
group by b.sample_datetime

quote:

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What is the proper term for this (in line view?) and where can I get more info?

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quote:

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How can I hold a resultset for a subsequent query?

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