The database automatically creates a separate (new) partition for every distinct partition key value of the table.

Auto-list partitioning removes the management burden from the DBAs to manually maintain a list of partitioned tables for a large number of distinct key values that require individual partitions. It also automatically copes with the unplanned partition key values without the need of a DEFAULT partition.

通过以下测试来简单验证一下这个特性的表征,如果是常规的列表分区，在分区缺失时会遇到ORA-14400错误：

SQL> CREATE TABLE enmotech (
  2    PartID	     integer	     not null,
  3    CretTm	     date	     not null,
  4    PartCD	     varchar2(2)     not null
  5  ) partition by list (partcd) (
  6    partition pBJ values ('BJ'),
  7    partition pCD values ('CD'),
  8    partition pGZ values ('GZ'),
  9    partition pSH values ('SH')
 10  );

Table created.

SQL> insert into enmotech values (1, sysdate, 'KM');
insert into enmotech values (1, sysdate, 'KM')
            *
ERROR at line 1:
ORA-14400: inserted partition key does not map to any partition

当设置了automatic关键字之后，分区变更为自动管理：

drop table enmotech purge;

CREATE TABLE enmotech (
  PartID	integer		not null,
  CretTm	date		not null,
  PartCD	varchar2(2)	not null
) partition by list (partcd) automatic (
  partition pBJ values ('BJ'),
  partition pCD values ('CD'),
  partition pGZ values ('GZ'),
  partition pSH values ('SH')
);

当插入一条未定义的分区数据时，新的分区被自动创建：

SQL> insert into enmotech values (1, sysdate, 'KM');

1 row created.

SQL> select partition_name from   user_tab_partitions
  2  where  table_name = 'ENMOTECH';

PARTITION_NAME
----------------------------------------------------
PBJ
PCD
PGZ
PSH
SYS_P290

如果这个自动分片的分区名不符合你的命名规则，可以通过DDL语句去修改变更：

SQL> alter table enmotech rename partition SYS_P290 to pKM;

Table altered.

SQL> select partition_name from   user_tab_partitions
  2  where  table_name = 'ENMOTECH';

PARTITION_NAME
---------------------------------------------------
PBJ
PCD
PGZ
PKM
PSH

对于已有的分区定义，可以通过关键字 automatic 和 manual 来进行分区定义的调整：

alter table PEOPLE set partitioning automatic;

alter table PEOPLE set partitioning manual;

这是Oracle Database 12.2 分区特性的众多增强之一。