学步园

Merging Partitions

使用ALTER TABLE .. MERGE PARTITION语句将两个分区的内容合并到另外一个分区，两个源分区和关联的local index都会被drop
　　不能用于 hash分区表或 hash subpartitions of a composite *-hash partitioned table
　　不能用于合并引用分区表(reference-partitioned table)
合并范围分区
　　允许合并两个临近范围的分区到另外分区，不相邻分区无法合并。合并结果分区继承两个源分区的最大边界。
demo:

-- Create a Table with four partitions each on its own tablespace
-- Partitioned by range on the data column.
CREATE TABLE four_seasons
( 
        one DATE,
        two VARCHAR2(60),
        three NUMBER
)
PARTITION  BY RANGE ( one ) 
(
PARTITION quarter_one 
   VALUES LESS THAN ( TO_DATE('01-apr-1998','dd-mon-yyyy'))
   TABLESPACE quarter_one,

PARTITION quarter_two 
   VALUES LESS THAN ( TO_DATE('01-jul-1998','dd-mon-yyyy'))
   TABLESPACE quarter_two,

PARTITION quarter_three
   VALUES LESS THAN ( TO_DATE('01-oct-1998','dd-mon-yyyy'))
   TABLESPACE quarter_three,

PARTITION quarter_four
   VALUES LESS THAN ( TO_DATE('01-jan-1999','dd-mon-yyyy'))
   TABLESPACE quarter_four

);

-- Create local PREFIXED index on Four_Seasons
-- Prefixed because the leftmost columns of the index match the
-- Partitioning key CREATE INDEX i_four_seasons_l ON four_seasons ( one,two ) 
LOCAL ( 
PARTITION i_quarter_one TABLESPACE i_quarter_one,
PARTITION i_quarter_two TABLESPACE i_quarter_two,
PARTITION i_quarter_three TABLESPACE i_quarter_three,
PARTITION i_quarter_four TABLESPACE i_quarter_four
);

下一步，合并分区.

-- Merge the first two partitions 
--
ALTER TABLE four_seasons 
MERGE PARTITIONS quarter_one, quarter_two INTO PARTITION quarter_two
UPDATE INDEXES;

如果不显式声明 UPDATE INDEXES 语句,就必须给受影响的分区 rebuild the local index.

-- Rebuild index for quarter_two, which has been marked unusable 
-- because it has not had all of the data from Q1 added to it.
-- Rebuilding the index will correct this.
--
ALTER TABLE four_seasons MODIFY PARTITION 
quarter_two REBUILD UNUSABLE LOCAL INDEXES;

合并Interval Partitions 

同RANGE一样，必须两个相邻分区才能合并
合并 List partitions则没有限制