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Altering and Managing Partition Tables

ALTERING PARTITION TABLES

To add a partition

You can add add a new partition to the "high" end (the point after the last existing partition). To add a partition
at the beginning or in the middle of a table, use the SPLIT PARTITION clause.

For example to add a partition to sales table give the following command.

alter table sales add partition p6 values less than (1996);

To add a partition to a Hash Partition table give the following command.

alter table products add partition;

Then Oracle adds a new partition whose name is system generated and it is created in the default tablespace.
To add a partition by user define name and in your specified tablespace give the following command.

alter table products add partition p5 tablespace u5;

To add a partition to a List partition table give the following command.

alter table customers add partition central_India
            values (‘BHOPAL’,’NAGPUR’);

Any value in the set of literal values that describe the partition(s) being added must not exist in any of the other partitions of the table.

Coalescing Partitions

Coalescing partitions is a way of reducing the number of partitions in a hash-partitioned table, or the number of subpartitions in a composite-partitioned table. When a hash partition is coalesced, its contents are redistributed into one or more remaining partitions determined by the hash function. The specific partition that is coalesced is selected by Oracle, and is dropped after its contents have been redistributed.

To coalesce a hash partition give the following statement.

alter table products coalesce partition;

This reduces by one the number of partitions in the table products.

DROPPING PARTITIONS

To drop a partition from Range Partition table, List Partition or Composite Partition table give the following command.

alter table sales drop partition p5;

Once you have drop the partition and if you have created a global index on the table. Then you have to rebuild the global index after dropping the partition by giving the following statement.

alter index sales_ind rebuild;

To avoid rebuilding of indexes after dropping of the partitions you can also first delete all the records and then drop
the partition like this

delete from sales where year=1994;

alter table sales drop partition p4;

This method is most appropriate for small tables, or for large tables when the partition being dropped contains a small percentage of the total data in the table.

Another method of dropping partitions is give the following statement.

ALTER TABLE sales DROP PARTITION p5 UPDATE GLOBAL INDEXES;

This causes the global index to be updated at the time the partition is dropped.

Exchanging a Range, Hash, or List Partition

To exchange a partition of a range, hash, or list-partitioned table with a nonpartitioned table, or the reverse, use the ALTER TABLE ... EXCHANGE PARTITION statement. An example of converting a partition into a nonpartitioned table follows. In this example, table stocks can be range, hash, or list partitioned.

ALTER TABLE stocks
    EXCHANGE PARTITION p3 WITH stock_table_3;

Merging Partitions

Use the ALTER TABLE ... MERGE PARTITIONS statement to merge the contents of two partitions into one partition. Te two original partitions are dropped, as are any corresponding local indexes.

You cannot use this statement for a hash-partitioned table or for hash subpartitions of a composite-partitioned table.

You can only merged two adjacent partitions, you cannot merge non adjacent partitions.

For example the merge the partition p2 and p3 into one partition p23 give the following statement.

alter table sales merge partition p2 and p3 into partition p23;

Modifying Partitions: Adding Values

Use the MODIFY PARTITION ... ADD VALUES clause of the ALTER TABLE statement to extend the value list of an existing partition. Literal values being added must not have been included in any other partition's value list. The partition value list for any corresponding local index partition is correspondingly extended, and any global index, or global or local index partitions, remain usable.

The following statement adds a new set of cities ('KOCHI', 'MANGALORE') to an existing partition list.

ALTER TABLE customers
   MODIFY PARTITION south_india
      ADD VALUES ('KOCHI', 'MANGALORE');

Modifying Partitions: Dropping Values

Use the MODIFY PARTITION ... DROP VALUES clause of the ALTER TABLE statement to remove literal values from the value list of an existing partition. The statement is always executed with validation, meaning that it checks to see if any rows exist in the partition that correspond to the set of values being dropped. If any such rows are found then Oracle returns an error message and the operation fails. When necessary, use a DELETE statement to delete corresponding rows from the table before attempting to drop values.

You cannot drop all literal values from the value list describing the partition. You must use the ALTER TABLE ... DROP PARTITION statement instead. 

The partition value list for any corresponding local index partition reflects the new value list, and any global index, or global or local index partitions, remain usable.

The statement below drops a set of cities (‘KOCHI' and 'MANGALORE') from an existing partition value list.

ALTER TABLE customers
   MODIFY PARTITION south_india
      DROP VALUES (‘KOCHI’,’MANGALORE’);

SPLITTING PARTITIONS

You can split a single partition into two partitions. For example to split the partition p5  of sales table into two partitions give the following command

alter table sales split partition p5 into
  (Partition p6 values less than (1996),
   Partition p7 values less then (MAXVALUE));

TRUNCATING PARTITON

Truncating a partition will delete all rows from the partition.

To truncate a partition give the following statement

alter table sales truncate partition p5;

 

 


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