SELECT data based on partitions

Question

I know we have PARTITION clause in SELECT statement.
My requirement is i need to select data from Last two partitions in which data is available.
If we know the name of the 2 partitions then we can select and UNION ALL.
But In my case, i dont know the partitition names too,
I need to find out the names of the partitions using any subquery and i need to select from that.
May i know how can i achieve this?
Thanks

Answer 1

Maybe you could adjust the below (NOT TESTED !) if the meaning of the recent 2 partitions is somehow connected with partition_position within [url http://download.oracle.com/docs/cd/E11882_01/server.112/e25513/statviews_2108.htm#REFRN20281]all_tab_partitions as I don't have a database at hand to find out how partitions are being numbered.
declare
  the_sql   varchar2(32000) := q'{ your sql here }'; -- assumed having a where clause
  the_table varchar2(30)    := 'your_table_name';
begin
  for i in (select partition_name
              from all_tab_partitions
             where table_name = the_table
               and partition_position <= 2  -- assumed ascending order for partition numbering
  for i in (select partition_name
              from (select partition_name,row_number() over (order by partition_position desc) rn
                      from all_tab_partitions
                     where table_name = the_table
             where rn <= 2  -- assumed descending order for partition numbering
  loop
    substr(the_sql,1,instr(the_sql,'where')) || ' partition (' || i.partition_name || ') ' ||
    substr(the_sql,instr(the_sql,'where')) || ' union all ';
  end loop;
  the_sql := 'select * from (' || substr(the_sql,1,instr(the_sql,' union all ',-1,1)) || ')';
  dbms_output(the_sql);
end;Regards
Etbin