Query to get last N used partitions.

Question

Hi,
I have a day based partitioned table TAB1.
Let say for month Aug 2013 Partitons are like P010813,P020813,P030813 up to P310813.
When gather stats job will run i want to analyze only the last 3 used partitions based on current date, this would be P180813,P190813,P200813.
Please help me to write a query which will give the last 3 used partitions.
eg.
If run query on 20-AUG-2013.
P180813
P190813
P200813
FOR 25-AUG-2013
P230813
P240813
P250813
Thanks

Answer 1

first about query : here is example
with t(a) as (
select 'P170813' from dual union all
select 'P180813' from dual union all
select 'P190813' from dual union all
select 'P200813' from dual union all
select 'P210813' from dual union all
select 'P220813' from dual union all
select 'P230813' from dual union all
select 'P240813' from dual union all
select 'P250813' from dual union all
select 'P260813' from dual union all
select 'P270813' from dual union all
select 'P280813' from dual union all
select 'P290813' from dual union all
select 'P300813' from dual union all
select 'P310813' from dual )
select * from(
select a, row_number() over(order by a desc) rn
  from t
where to_date((replace(a, 'P', '')),'ddmmyy') <= trunc(sysdate)
) q
where q.rn <= 3
but i think you don't need query and etc. read documentation about DBMS_STATS.SET_SCHEMA_PREFS  and look at parameters INCREMENTAL, STALE_PERCENT
Ramin Hashimzade