Dynamically selecting partitions - oracle

Question

I have a table with a few hundred partitions and I am generally interested on the latest 35.
Accordingly I am trying to create views which would access these dynamically. i.e. always use the latest in case ones are created.
The query:
select PARTITION_NAME,
PARTITION_POSITION,
NUM_ROWS,
AVG_ROW_LEN
from all_tab_partitions
where
table_name = 'MY_TABLE'
AND PARTITION_NAME <> 'P_LAST'
AND PARTITION_POSITION < (SELECT MAX(PARTITION_POSITION)
FROM all_tab_partitions) - 35
order by 2 DESC
;
Seems to return me the partition names I'm interested, however, I don't manage to use it's results to select the partitions. e.g.:
CREATE OR REPLACE VIEW MY_VIIEW AS
WITH t AS ( [Above query] )
SELECT * FROM
MY_TABLE PARTITION (SELECT /*+ FIRST_ROWS(1) */ PARTITION_NAME
from t);
(not the actual view, just an example)
So how do I do that? How do I create a view which will acess always the latest partition (execpt of "MAX")?
I am using Oracle 10g
thanks

Answer 1

You can do it using PL/SQL only
create or replace package my_table_ is
type t_records is table of my_table%rowtype;
function getpart(c_parts sys_refcursor) return t_records pipelined;
end;
create or replace package body my_table_ is
function getpart(c_parts sys_refcursor) return t_records pipelined is
v_partition all_tab_partitions.partition_name%type;
v_row my_table%rowtype;
c_mytab sys_refcursor;
begin
loop
fetch c_parts into v_partition;
exit when c_parts%notfound;
open c_mytab for 'select * from my_table partition ('||v_partition||')';
loop
fetch c_mytab into v_row;
exit when c_mytab%notfound;
pipe row (v_row);
end loop;
end loop;
end;
end;
Now you can
select * from table(my_table_.getpart(cursor(<QUERY_RETURNING_PARTITION_NAMES>)));

Answer 2

May be you can construct view's query using batch of union all statements with partition name in each statement, e.g.
create view p as
select * from my_table partition (part1)
union all
select * from my_table partition (part1)
...
union all
select * from my_table partition (part35)

Answer 3

Ok... I don't think your can use the Partition-Names, but you can use the Starting-Values of the Partitions to select the Data matching these Partitions...
So you View would look like this:
SELECT * FROM my_table WHERE date_col > get_part_limit( 'my_table', 35 ):
Where date_col is the column you use for partitioning - and get_part_limit is a stored function you write like this:
...
BEGIN
SELECT high_value FROM all_tab_partitions
INTO local_var
WHERE table_name = parameter_name
AND PARTITION_POSITION = MAX... - 35
EXECUTE IMMEDIATE 'SELECT '||local_var||' FROM DUAL' INTO local_return_value;
RETURN local_return_value;
END;

Answer 4

partitions are designed to be transparent for the data, so when you write a query, you simply don't know how your data is stored.
I see only one possibility to hit a particular partition: your WHERE clause should match values to the partitioned columns of latest (or latest 5) partition.
Next question is to build this WHERE clause on the fly. You already know that there is plenty of information in oracle dictionary. So you will read that and create a constructor to convert metadata conditions back into SQL.

Answer 5

irl we do exactly the same thing and use falco's solution like.
Here is my code:
create or replace function longToDate( myOwner varchar2,
mytable_name in varchar2,
mypartition_name in varchar2
) return date
as
cDate date;
cvar varchar2(1024);
rq varchar2(1024);
infiniteValue EXCEPTION;
PRAGMA EXCEPTION_INIT(infiniteValue, -00904);
begin
select high_value into cvar FROM dba_tab_partitions t where t.table_owner=myOwner and table_name=mytable_name and partition_name=mypartition_name;
rq:='select '||cvar||' from dual';
execute immediate rq into cDate;
return cdate;
EXCEPTION
WHEN infiniteValue
then return'01 jan 3000';
when others
then return null;
end longToDate;
Ant the view is something like this
create or replace view last_35 as
with maxdate as
(select longToDate(p.table_owner,p.table_name,p.partition_name) mydate,
rank()over(order by p.partition_position desc) mypos,
p.* from all_tab_partitions p
where p.table_name='MY_TABLE'
)
select /*+full(a)*/* from MY_TABLE a, maxdate
where MY_TABLE.partition_name>maxdate.mydate
and maxdate.mypos=35