1、准备测试表

SQL> create table t_d as select * from all_objects;
Table created
SQL> alter table t_d add primary key(object_id);
Table altered
SQL> create table t_d_t as select * from t_d where 1=0;
Table created
SQL> alter table t_d_t add primary key(object_id);
Table altered
SQL> select count(*) from T_D;
  COUNT(*)
----------
     48945
SQL> select count(*) from T_D_T;
  COUNT(*)
----------
     0

2、执行在线同步

SQL> EXEC DBMS_REDEFINITION.CAN_REDEF_TABLE(user, 'T_D', DBMS_REDEFINITION.CONS_USE_PK);
PL/SQL procedure successfully completed
SQL> EXEC DBMS_REDEFINITION.START_REDEF_TABLE(USER, 'T_D', 'T_D_T');
PL/SQL procedure successfully completed
 

3、查询相关物化视图

SQL> select owner,mview_name from user_mviews;
OWNER                          MVIEW_NAME
------------------------------ ------------------------------
CHF                            T_D_T
SQL> select log_owner,master,log_table from user_mview_logs;
LOG_OWNER                      MASTER                         LOG_TABLE
------------------------------ ------------------------------ ------------------------------
CHF                            T_D                            MLOG$_T_D
CREATE MATERIALIZED VIEW T_D_T
ON PREBUILT TABLE
REFRESH FAST ON DEMAND
AS
SELECT "T_D"."OWNER" "OWNER","T_D"."OBJECT_NAME" "OBJECT_NAME",
"T_D"."SUBOBJECT_NAME" "SUBOBJECT_NAME","T_D"."OBJECT_ID" "OBJECT_ID",
"T_D"."DATA_OBJECT_ID" "DATA_OBJECT_ID","T_D"."OBJECT_TYPE" "OBJECT_TYPE",
"T_D"."CREATED" "CREATED","T_D"."LAST_DDL_TIME" "LAST_DDL_TIME",
"T_D"."TIMESTAMP" "TIMESTAMP","T_D"."STATUS" "STATUS",
"T_D"."TEMPORARY" "TEMPORARY","T_D"."GENERATED" "GENERATED",
"T_D"."SECONDARY" "SECONDARY" FROM "CHF"."T_D" "T_D";

4、结束物化视图

SQL> EXEC DBMS_REDEFINITION.FINISH_REDEF_TABLE(USER, 'T_D', 'T_D_T');
PL/SQL procedure successfully completed

5、继续查询相关物化视图

SQL>  select log_owner,master,log_table from user_mview_logs;
SQL> select * from user_mviews;
SQL> select owner,mview_name from user_mviews;
OWNER                          MVIEW_NAME
------------------------------ ------------------------------
SQL> select log_owner,master,log_table from user_mview_logs;
LOG_OWNER                      MASTER                         LOG_TABLE
------------------------------ ------------------------------ ------------------------
SQL> select count(*) from T_D_T;
  COUNT(*)
----------
     48945

6、由试验可以得出
6.1)在线重定义本质就是利用物化视图刷新实现数据迁移
6.2)DBMS_REDEFINITION.START_REDEF_TABLE实现功能：
6.2.1)创建含on prebuilt table的物化视图和物化视图日志
6.2.2)实现通过物化视图刷新当前表中数据进入中间表
6.3)dbms_redefinition.sync_interim_table实现物化视图刷新在执行5.2）操作过程中变化数据
6.4)DBMS_REDEFINITION.FINISH_REDEF_TABLE将锁定原表，防止表上的DML,物化视图执行刷新，完成刷新后，将删除物化视图和对应的日志，将中间表rename成目标表

7、如果表无主键时，区别有
7.1）执行在线定义语句，具体见表在线重定义(无主键)
7.2）创建物化视图语句上

create materialized view T_D_T
on prebuilt table
refresh fast on demand
with rowid
as
select OWNER OWNER,
OBJECT_NAME OBJECT_NAME,
 SUBOBJECT_NAME SUBOBJECT_NAME,
 OBJECT_ID OBJECT_ID,
 DATA_OBJECT_ID DATA_OBJECT_ID,
 OBJECT_TYPE OBJECT_TYPE,
 CREATED CREATED,
 LAST_DDL_TIME LAST_DDL_TIME,
 TIMESTAMP TIMESTAMP,
 STATUS STATUS,
 TEMPORARY TEMPORARY,
 GENERATED GENERATED,
 SECONDARY SECONDARY
 from "CHF"."T_D"   "T_D";

1、创建测试表
SQL> CREATE TABLE t_M
2 AS
3 SELECT * FROM all_objects;
Table created
2、查询测试表中记录
SQL> select count(*) from t_m;
COUNT(*)
———-
48941
3、创建中间表
SQL> create table t_m_n as
2 select * from t_m where 1=0;
Table created
4、查询中间表记录
SQL> select count(*) from t_m_n;
COUNT(*)
———-
5、创建刷新物化视图
SQL> CREATE MATERIALIZED VIEW t_m_n
on prebuilt TABLE WITH REDUCED PRECISION
REFRESH FORCE
ON DEMAND
AS
SELECT * FROM t_m;
Materialized view created
6、执行物化视图刷新
SQL> exec dbms_mview.refresh(‘T_M_N’);
PL/SQL procedure successfully completed
7、查询物化视图中记录数
SQL> select count(*) from t_m_n;
COUNT(*)
———-
48941
8、删除物化视图
SQL> DROP MATERIALIZED VIEW T_M_N;
Materialized view dropped
9、查询中间表中条数
SQL> select count(*) from t_m_n;
COUNT(*)
———-
48941
10、后续可能操作
1）t_m和t_m_n相互重命名，实现在线修移动表的位置、改表结构、降低高水位等操作，同（shrink）
2）和dblink结合，实现数据的跨版本迁移