Split partition

Question

hi
Oracle 10.2.0.1.0
from the link http://www.rampant-books.com/t_ault_39_partitions_alter_table.htm there is info like
Modifying Table Partitions
You can modify a table or table partition in any of the ways described in the subsections following. You cannot combine partition operations with other partition operations or with operations on the base table in one ALTER TABLE statement. You cannot move a partition with subpartitions; each subpartition must be individually moved.    
Add Partition. Use ALTER TABLE ADD PARTITION to add a partition to the high end of the table (after the last existing partition). If the first element of the partition bound of the high partition is MAXVALUE, you cannot add a partition to the table. You must split the high partition.     
You can add a partition to a table even if one or more of the table indexes or index partitions are marked UNUSABLE.     
_*You must use the SPLIT PARTITION clause to add a partition at the beginning or the middle of the table.*_     can you please elaborate in the text above and why should we use split partition instead of add partition ? how can one know where the partition is being added like in beginning , middle etc ... how the concept of partition is handled .
please help

Answer 1

To further clarify, 'highest partition' is determined by the partition that can take the highest value of your partitioning key.
Your table DDL, when specifying the partitions, would specify the partition limits something like this:
PARTITION BY RANGE (EFFECTIVE_DATE)
  PARTITION PART_201005 VALUES LESS THAN (TO_DATE('2010-06-01', 'YYYY-MM-DD')),
  PARTITION PART_201006 VALUES LESS THAN (TO_DATE('2010-07-01', 'YYYY-MM-DD')),
  PARTITION PART_201007 VALUES LESS THAN (TO_DATE('2010-08-01', 'YYYY-MM-DD')),
  PARTITION PART_201008 VALUES LESS THAN (TO_DATE('2010-09-01', 'YYYY-MM-DD')),
  PARTITION PART_201009 VALUES LESS THAN (TO_DATE('2010-10-01', 'YYYY-MM-DD')),
  PARTITION PART_201010 VALUES LESS THAN (TO_DATE('2010-11-01', 'YYYY-MM-DD')),
  PARTITION PART_201011 VALUES LESS THAN (TO_DATE('2010-12-01', 'YYYY-MM-DD')),
  PARTITION PART_201012 VALUES LESS THAN (TO_DATE('2011-01-01', 'YYYY-MM-DD')),
  PARTITION PART_201101 VALUES LESS THAN (TO_DATE('2011-02-01', 'YYYY-MM-DD'))
)Now, you can
ALTER TABLE whatever ADD PARTITION PART_201102 VALUES LESS THAN  (TO_DATE('2011-03-01', 'YYYY-MM-DD'));because you are adding a partition higher than all the existing partitions.
But you can not
ALTER TABLE whatever ADD PARTITION PART_201004 VALUES LESS THAN  (TO_DATE('2010-05-01', 'YYYY-MM-DD'));because data eligible for that partition would already be eligible for (and possibly stored in) PART_201005. You would instead have to split partition PART_201005:
ALTER TABLE whatever SPLIT PARTITION PART_201005
  AT   (TO_DATE('2010-05-01', 'YYYY-MM-DD'))
  INTO (PART_201004 , PART_201005 );With an ADD PARTITION there is no data to move - because data that can go into the new partition could never have gotten into the table, in any partition, before it was added. But with a SPLIT PARTITION the data must be checked and moved if necessary.
Edited by: mtefft on Jan 20, 2011 10:20 AM (removed extraneous spaces)