Apress.Expert.Oracle.Database.Architecture.9i.and.10g.Programming.Techniques.and.Solutions.Sep.2005

CHAPTER 13 ■ PARTITIONING 577
We would have to remove the DEFAULT partition, then add PART_4, and then put the
DEFAULT partition back. The reason behind this is that the DEFAULT partition could have had
rows with the list partition key value of CA or NM—they would not belong in the DEFAULT partition
after adding PART_4.
Composite Partitioning
Lastly, we’ll look at some examples of composite partitioning, which is a mixture of range and
hash or range and list.
In composite partitioning, the top-level partitioning scheme is always range partitioning.
The secondary level of partitioning is either list or hash (in Oracle9i Release 1 and earlier only
hash subpartitioning is supported, not list). It is interesting to note that when you use composite
partitioning, there will be no partition segments—there will be only subpartition
segments. When using composite partitioning, the partitions themselves do not have segments
(much like a partitioned table doesn’t have a segment). The data is physically stored in
subpartition segments and the partition becomes a logical container, or a container that
points to the actual subpartitions.
In our example, we’ll look at a range-hash composite. Here we are using a different set of
columns for the range partition from those used for the hash partition. This is not mandatory;
we could use the same set of columns for both:
ops$tkyte@ORA10G> CREATE TABLE composite_example
2 ( range_key_column date,
3 hash_key_column int,
4 data varchar2(20)
5 )
6 PARTITION BY RANGE (range_key_column)
7 subpartition by hash(hash_key_column) subpartitions 2
8 (
9 PARTITION part_1
10 VALUES LESS THAN(to_date('01/01/2005','dd/mm/yyyy'))
11 (subpartition part_1_sub_1,
12 subpartition part_1_sub_2
13 ),
14 PARTITION part_2
15 VALUES LESS THAN(to_date('01/01/2006','dd/mm/yyyy'))
16 (subpartition part_2_sub_1,
17 subpartition part_2_sub_2
18 )
19 )
20 /
Table created.
In range-hash composite partitioning, Oracle will first apply the range partitioning rules
to figure out which range the data falls into. Then it will apply the hash function to decide
into which physical partition the data should finally be placed. This process is described in
Figure 13-4.