昨天介绍了PostgreSQL里的继承表，明天来持续探讨ORACLE数据库里有没有相似的货色。

首先，能够明确的说，ORACLE数据库里没有继承表这种OBJECT。
然而，和PostgreSQL的继承表相似，不同Table的数据以某种形式进行关联，共享存储空间的角度来讲，ORACLE数据库也存在这样的OBJECT。

那就是CLUSTER。

首先，ORACLE数据库对“CLUSTER”是这样定义的：

CREATE CLUSTER (oracle.com)A cluster is a schema object that contains data from one or more tables.

上面咱们来看看CLUSTER是怎么利用的。

--做成CLUSTERSQL> conn test/test@localhost:1521/pdb接続されました。SQL> CREATE CLUSTER object   (object VARCHAR2(23))SIZE 512STORAGE (initial 100K next 50K);  2    3    4クラスタが作成されました。--为CLUSTR做一个索引SQL> CREATE INDEX idx_object ON CLUSTER object;索引が作成されました。--做成应用CLUSTER的第一个表SQL> CREATE TABLE object_table   CLUSTER object (OBJECT_TYPE)   AS SELECT * FROM dba_objects WHERE OBJECT_TYPE = 'TABLE';  2    3表が作成されました。--做成应用CLUSTER的第二个表SQL> CREATE TABLE object_index   CLUSTER object (OBJECT_TYPE)   AS SELECT * FROM dba_objects WHERE OBJECT_TYPE = 'INDEX';  2    3表が作成されました。--确认一下两个表的状态和定义SQL> select count(*) from object_index;  COUNT(*)----------      2898SQL> select count(*) from object_table;  COUNT(*)----------      2223SQL> @objobject_nameに値を入力してください: object_index旧   1: select owner,object_name,object_type from dba_objects where object_name like upper('&object_name')新   1: select owner,object_name,object_type from dba_objects where object_name like upper('object_index')OWNER                OBJECT_NAME                                        OBJECT_TYPE-------------------- -------------------------------------------------- -----------------------TEST                 OBJECT_INDEX                                       TABLESQL> @objobject_nameに値を入力してください: object_table旧   1: select owner,object_name,object_type from dba_objects where object_name like upper('&object_name')新   1: select owner,object_name,object_type from dba_objects where object_name like upper('object_table')OWNER                OBJECT_NAME                                        OBJECT_TYPE-------------------- -------------------------------------------------- -----------------------TEST                 OBJECT_TABLE                                       TABLESQL> @ddlobject_typeに値を入力してください: TABLEobject_nameに値を入力してください: OBJECT_INDEXownerに値を入力してください: TEST旧   1: select dbms_metadata.get_ddl('&object_type','&object_name','&owner') from dual新   1: select dbms_metadata.get_ddl('TABLE','OBJECT_INDEX','TEST') from dualDBMS_METADATA.GET_DDL('TABLE','OBJECT_INDEX','TEST')--------------------------------------------------------------------------------  CREATE TABLE "TEST"."OBJECT_INDEX"   (    "OWNER" VARCHAR2(128),        "OBJECT_NAME" VARCHAR2(128),        "SUBOBJECT_NAME" VARCHAR2(128),        "OBJECT_ID" NUMBER,        "DATA_OBJECT_ID" NUMBER,        "OBJECT_TYPE" VARCHAR2(23),        "CREATED" DATE,        "LAST_DDL_TIME" DATE,        "TIMESTAMP" VARCHAR2(19),        "STATUS" VARCHAR2(7),        "TEMPORARY" VARCHAR2(1),        "GENERATED" VARCHAR2(1),        "SECONDARY" VARCHAR2(1),        "NAMESPACE" NUMBER,        "EDITION_NAME" VARCHAR2(128),        "SHARING" VARCHAR2(18),        "EDITIONABLE" VARCHAR2(1),        "ORACLE_MAINTAINED" VARCHAR2(1),        "APPLICATION" VARCHAR2(1),        "DEFAULT_COLLATION" VARCHAR2(100),        "DUPLICATED" VARCHAR2(1),        "SHARDED" VARCHAR2(1),        "CREATED_APPID" NUMBER,        "CREATED_VSNID" NUMBER,        "MODIFIED_APPID" NUMBER,        "MODIFIED_VSNID" NUMBER   ) CLUSTER "TEST"."OBJECT" ("OBJECT_TYPE")SQL> @ddlobject_typeに値を入力してください: TABLEobject_nameに値を入力してください: OBJECT_TABLEownerに値を入力してください: TEST旧   1: select dbms_metadata.get_ddl('&object_type','&object_name','&owner') from dual新   1: select dbms_metadata.get_ddl('TABLE','OBJECT_TABLE','TEST') from dualDBMS_METADATA.GET_DDL('TABLE','OBJECT_TABLE','TEST')--------------------------------------------------------------------------------  CREATE TABLE "TEST"."OBJECT_TABLE"   (    "OWNER" VARCHAR2(128),        "OBJECT_NAME" VARCHAR2(128),        "SUBOBJECT_NAME" VARCHAR2(128),        "OBJECT_ID" NUMBER,        "DATA_OBJECT_ID" NUMBER,        "OBJECT_TYPE" VARCHAR2(23),        "CREATED" DATE,        "LAST_DDL_TIME" DATE,        "TIMESTAMP" VARCHAR2(19),        "STATUS" VARCHAR2(7),        "TEMPORARY" VARCHAR2(1),        "GENERATED" VARCHAR2(1),        "SECONDARY" VARCHAR2(1),        "NAMESPACE" NUMBER,        "EDITION_NAME" VARCHAR2(128),        "SHARING" VARCHAR2(18),        "EDITIONABLE" VARCHAR2(1),        "ORACLE_MAINTAINED" VARCHAR2(1),        "APPLICATION" VARCHAR2(1),        "DEFAULT_COLLATION" VARCHAR2(100),        "DUPLICATED" VARCHAR2(1),        "SHARDED" VARCHAR2(1),        "CREATED_APPID" NUMBER,        "CREATED_VSNID" NUMBER,        "MODIFIED_APPID" NUMBER,        "MODIFIED_VSNID" NUMBER   ) CLUSTER "TEST"."OBJECT" ("OBJECT_TYPE")--确认一下两个表的存储状况col OWNER for a10col SEGMENT_NAME for a20col SEGMENT_TYPE for a18col SEGMENT_SUBTYPE for a10col TABLESPACE_NAME for a10col RETENTION for a7set lin 200 pages 999select OWNER,SEGMENT_NAME,SEGMENT_TYPE,SEGMENT_SUBTYPE,TABLESPACE_NAME,HEADER_FILE,HEADER_BLOCK,BLOCKS,EXTENTS,RETENTION from dba_segments where OWNER='TEST';OWNER      SEGMENT_NAME         SEGMENT_TYPE       SEGMENT_SU TABLESPACE HEADER_FILE HEADER_BLOCK     BLOCKS    EXTENTS RETENTI---------- -------------------- ------------------ ---------- ---------- ----------- ------------ ---------- ---------- -------TEST       OBJECT               CLUSTER            ASSM       USERS               12          130         96         12TEST       IDX_OBJECT           INDEX              ASSM       USERS               12          146          8          1

OK，曾经能够确认到应用CLUSTER的两张表的确共享了存储空间。

当然，ORACLE数据库的CLUSTER和PostgreSQL继承表并不是雷同的货色，下面的例子只是从多张表共享物理存储空间的角度进行了剖析,至于其余的角度，就见仁见智了。

2021/06/18 @ Dalian