对Oracle表分区的一点认识
Oracle的表分区功能通过改善可管理性、性能和可用性,从而为各式应用程序带来了极大的好处。通常,分区可以使某些查询以及维护操
Oracle的表分区功能通过改善可管理性、性能和可用性,从而为各式应用程序带来了极大的好处。通常,分区可以使某些查询以及维护操作的性能大大提高。此外,分区还可以极大简化常见的管理任务,分区是构建千兆字节数据系统或超高可用性系统的关键工具。
分区功能能够将表、索引或索引组织表进一步细分为段,这些数据库对象的段叫做分区。每个分区有自己的名称,还可以选择自己的存储特性。从数据库管理员的角度来看,一个分区后的对象具有多个段,这些段既可进行集体管理,也可单独管理,这就使数据库管理员在管理分区后的对象时有相当大的灵活性。但是,从应用程序的角度来看,分区后的表与非分区表完全相同,使用 SQL DML 命令访问分区后的表时,无需任何修改。
比较能理解的是以下几个几种表分区:
1 范围分区
每个分区都由一个分区键值范围指定create table RangeTable(
id int primary key,
name varchar(10),
grade int
)
partition by rang(grade)
(
partition part1 values less then(1000) tablespace Part1_tb,
partition part2 values less then(MAXVALUE) tablespace Part2_tb
);
2 列表分区
create table ListTable(
id int primary key,
name varchar(20),
area varchar(10)
)
partition by list(area)
(
partition part1 values('guangdong','beijing') tablespace Part1_tb,
partition part2 values('shanghai','nanjing') tablespace Part2_tb
);
3 散列分区
create table HashTable(
id int primary key,
name varchar(20),
grade int
)
partition by hash(grade)
partitions 10
store in(Part1_tb,Part2_tb,Part3_tb)
partition by rang(grade)(
partition part1 tablespace Part1_tb,
partition part2 tablespace Part2_tb
);
4 索引分区
create index IndexTable_index
on IndexTable(name)
local
(
partition part1 tablespace Part1_tb,
partition part2 tablespace Part2_tb
)--local 告诉oracle表 IndexTable的每一个分区建立一个独立的索引
create index IndexTable_index
on IndexTable(name)
global;
--global为全局索引 全局索引可以包含多个分区的值 局部索引比全局索引容易管理,而全局索引比较快
注意:不能为散列分区 或者 子分区创建全局索引。

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