SQL Oracle---get last record for every month - sql

Question

I have a table that contain some Inspection Data. Every commodity needs to be inspected every month. The goal here is to find the last inspected record for each month.
Table Inspection:
INSPECTION_I--------INSPECTION_TS
200--------------------------- 10/20/2011
201----------------------------10/24/2011
202----------------------------10/26/2011
Table Product_Inspection:
INSPECTION_I------------------ASSET_I
200------------------------------------1000
201------------------------------------2000
Table Box_Inspection
INSPECTION_I--------ASSET_I
202------------------------3000
Table Product
ASSET_I------------ASSOCIATED_BOX_ASSET_I
1000---------------------------3000
Table BOX:
ASSET_I------------OTHER_STUFF
3000--------------------#####
Now in this case what I want is 201 and not 200. I tried to do MAX(to_char(inspection_ts, 'mm/yyyy')) but that is not helping. There is one more issue. For some reason, I keep getting the Cartesian in a case where a Product or a Box is inspected twice or more in a month. All I want is one inspection every month and it should be the last inspection for each month. I am really close to getting it but if someone can help, I would really appreciate it. I was able to get it done through a nested cursor but I don't want that.

Answer 1

I tend to use analytic functions to do this kind of query. Something like:
with data as
(
select 1 product_id, 100 inspection_id, to_date('09/04/2011', 'MM/DD/YYYY') inspection_date from dual union all
select 1 product_id, 101 inspection_id, to_date('09/14/2011', 'MM/DD/YYYY') inspection_date from dual union all
select 1 product_id, 103 inspection_id, to_date('10/04/2011', 'MM/DD/YYYY') inspection_date from dual union all
select 1 product_id, 105 inspection_id, to_date('11/01/2011', 'MM/DD/YYYY') inspection_date from dual union all
select 2 product_id, 102 inspection_id, to_date('09/24/2011', 'MM/DD/YYYY') inspection_date from dual union all
select 2 product_id, 104 inspection_id, to_date('10/05/2011', 'MM/DD/YYYY') inspection_date from dual
)
select *
from
(
select
product_id,
inspection_id,
inspection_date,
row_number() over (
partition by
product_id,
trunc(inspection_date, 'MM') -- Month
order by
inspection_date desc
) rn
from
data
)
where rn = 1 -- indicates last inspection date of the month for each product

Answer 2

use a subquery
Select [ColName List]
From TableName a
Where DateTimeColumname
= (Select Max(DateTimeColumnName)
From TableName
Where DateTimeColumnName < 1+Last_Day(a.DateTimeColumnName))