How can I retrieve last month and last mont -1?

Question

Hi guys, I am finishing to build a complex SSIS package, the last task is pretty simple but I'd like you to suggest the better solution in terms of performance (table with millions rows). The task is to create two table, one with the last update (archived)
and one with the last update -1 (the update is done monthly) taking the data from an huge table (create by the package).
The DDL (sample):
create table forum (runner varchar(20), race varchar(20), nmonth varchar (6), archived datetime2)
insert into forum values ('Zabres','Poland Red Bull','201411','2015-01-26 11:37:02.6870000'),
('Reynolds','Poland Red Bull','201411','2015-01-26 11:36:02.6870000'),
('Greefer','Poland Red Bull','201411','2015-01-26 11:38:04.6870000'),
('Zabres','France Red Bull','201411','2015-01-26 11:38:10.6870000'),
('Reynolds','France Red Bull','201411','2015-01-26 11:36:02.6870000'),
('Greefer','France Red Bull','201411','2015-01-26 11:36:02.6870000'),
('Zabres','Poland Red Bull','201411','2014-12-31 16:22:02.6870000'),
('Reynolds','Poland Red Bull','201411','2014-12-31 16:26:02.6870000'),
('Greefer','Poland Red Bull','201411','2014-12-31 16:26:14.6870000'),
('Zabres','France Red Bull','201411','2014-12-31 16:22:02.6870000'),
('Reynolds','France Red Bull','201411','2014-12-31 16:22:02.6870000'),
('Greefer','France Red Bull','201411','2014-12-31 16:22:02.6870000'),
('Zabres','Poland Red Bull','201411','2014-12-11 10:30:14.5870000'),
('Reynolds','Poland Red Bull','201411','2014-12-11 10:31:10.5550000'),
('Greefer','Poland Red Bull','201411','2014-12-11 10:31:14.3560000'),
('Zabres','Poland Red Bull','201411','2014-12-11 9:11:14.4420000'),
('Reynolds','Poland Red Bull','201411','2014-12-11 9:11:54.7760000'),
('Greefer','Poland Red Bull','201411','2014-12-11 9:11:55.7860000')
The tough thing is the format of archived. How can I take the last month and, especially, the last month -1 without caring about the seconds and milliseconds ?
The expected is LAST MONTH
LAST MONTH -1
Many thanks in advance

Answer 1

Yes! Your solution looks better, even in terms of performance (242 sec mine, 202 sec yours). Now I'm wondering the same, shall I upload the elements only once per month? What if I got more upload in one month?
You can also upload it once per week
In which case query would be like
SELECT *
FROM forum
WHERE archived >= DATEADD(wk,DATEDIFF(wk,0,GETDATE()),0)
AND archived < DATEADD(wk,DATEDIFF(wk,0,GETDATE())+1,0)
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