说明：物化视图(Materialized Views)是查询的结果集，所有原表和视图的变更都将导致物化视图的失效，最近就发现了一个物化视图经常失效的问题，以下是整理的文档。

一、物化视图状态查询：ORACLE提供了一个视图用于查询物化视图的状态USER_MVIEWS,其中列STALENESS，用于显示当前物化视图的状态

Relationship between the contents of the materialized view and the contents of the materialized view's masters:FRESH- Materialized view is a read-consistent view of the current state of its masters(最新状态：当前物化视图的内容出于最新的状态)

STALE- Materialized view is out of date because one or more of its masters has changed. If the materialized view wasFRESHbefore it becameSTALE, then it is a read-consistent view of a former state of its masters.(陈旧状态：物化视图引用的主表已经更新，但是物化视图没有刷新，所以内容相对主表来说是旧的)

NEEDS_COMPILE- Some object upon which the materialized view depends has changed. AnALTER MATERIALIZED VIEW...COMPILEstatement is required to validate this materialized view and compute the staleness of the contents.(需要编译：物化视图引用的主表比如视图，进行了重建后相应的物化视图就需要编译，当处于这种状态的时候dba_objects视图显示的STATUS为INVALID)

需要运行语句:ALTER MATERIALIZED VIEW MV_NAME COMPILE;进行重新编译；

UNUSABLE- Materialized view is not a read-consistent view of its masters from any point in time(物化视图引用的主表状态不确定)

UNKNOWN- Oracle Database does not know whether the materialized view is in a read-consistent view of its masters from any point in time (this is the case for materialized views created on prebuilt tables)(未知：通过prebuilt创建的表)

UNDEFINED- Materialized view has remote masters. The concept of staleness is not defined for such materialized views.(物化视图引用的表来自其他的数据库，一般通过dblink链接过来的)

二、实验测试：

2.1  创建物化视图

CREATE MATERIALIZED VIEW MV_TEST (EMPNO,ENAME,JOB,MGR,HIREDATE,SAL,COMM,DEPTNO)

TABLESPACE USERS

PCTUSED 0

PCTFREE 10

INITRANS 2

MAXTRANS 255

STORAGE (

INITIAL 64K

NEXT 1M

MINEXTENTS 1

MAXEXTENTS UNLIMITED

PCTINCREASE 0

BUFFER_POOL DEFAULT

FLASH_CACHE DEFAULT

CELL_FLASH_CACHE DEFAULT

)

NOCACHE

LOGGING

NOCOMPRESS

NOPARALLEL

BUILD IMMEDIATE

USING INDEX

TABLESPACE USERS

PCTFREE 10

INITRANS 2

MAXTRANS 255

STORAGE (

INITIAL 64K

NEXT 1M

MINEXTENTS 1

MAXEXTENTS UNLIMITED

PCTINCREASE 0

BUFFER_POOL DEFAULT

FLASH_CACHE DEFAULT

CELL_FLASH_CACHE DEFAULT

)

REFRESH FORCE ON DEMAND

WITH PRIMARY KEY

AS

/* Formatted on 2014/12/30 16:36:55 (QP5 v5.215.12089.38647) */

SELECT "EMP"."EMPNO""EMPNO",

"EMP"."ENAME""ENAME",

"EMP"."JOB""JOB",

"EMP"."MGR""MGR",

"EMP"."HIREDATE""HIREDATE",

"EMP"."SAL""SAL",

"EMP"."COMM""COMM",

"EMP"."DEPTNO""DEPTNO"

FROM "SCOTT"."EMP""EMP"

WHERE "EMP"."DEPTNO"=20;

COMMENT ON MATERIALIZED VIEW MV_TEST IS 'snapshot table for snapshot SCOTT.MV_TEST';

CREATE UNIQUE INDEX PK_EMP1 ON MV_TEST

(EMPNO)

LOGGING

TABLESPACE USERS

PCTFREE 10

INITRANS 2

MAXTRANS 255

STORAGE (

INITIAL 64K

NEXT 1M

MINEXTENTS 1

MAXEXTENTS UNLIMITED

PCTINCREASE 0

BUFFER_POOL DEFAULT

FLASH_CACHE DEFAULT

CELL_FLASH_CACHE DEFAULT

)

NOPARALLEL;

2.2 查询当前物化视图的状态

SQL> SELECT mview_name,staleness FROM DBA_MVIEWS WHERE MVIEW_NAME='MV_TEST';

MVIEW_NAME               STALENESS

------------------------------ -------------------

MV_TEST                FRESH

2.3 查询数据库物化视图的状态

column OBJECT_NAME format a20;

column STATUS format a20; OBJECT_TYPE

column OBJECT_TYPE format a20;

SQL> select OBJECT_NAME,STATUS,OBJECT_TYPE from dba_objects where OBJECT_NAME='MV_TEST' ;

OBJECT_NAME         STATUS          OBJECT_TYPE

-------------------- -------------------- --------------------

MV_TEST          VALID          TABLE

MV_TEST          VALID          MATERIALIZED VIEW

2.4 修改源表的数据

SQL> SELECT mview_name,staleness FROM DBA_MVIEWS WHERE MVIEW_NAME='MV_TEST';

MVIEW_NAME               STALENESS

------------------------------ -------------------

MV_TEST                NEEDS_COMPILE

显示状态需要编译

SQL> ALTER MATERIALIZED VIEW SCOTT.MV_TEST COMPILE;

进行相应的编译

SQL>  SELECT mview_name,staleness FROM DBA_MVIEWS WHERE MVIEW_NAME='MV_TEST';

MVIEW_NAME               STALENESS

------------------------------ -------------------

MV_TEST                          STALE

编译完成后，状态变成STALE

2.5 修改源表的表结构测试

SQL>  ALTER TABLE SCOTT.EMP RENAME COLUMN COMM TO COMMS; //修改源表的结构

SQL> SELECT mview_name,staleness FROM DBA_MVIEWS WHERE MVIEW_NAME='MV_TEST';//查看物化视图的状态

MVIEW_NAME               STALENESS

------------------------------ -------------------

MV_TEST                NEEDS_COMPILE

SQL>  ALTER MATERIALIZED VIEW SCOTT.MV_TEST COMPILE; //重新编译

SQL>  SELECT mview_name,staleness FROM DBA_MVIEWS WHERE MVIEW_NAME='MV_TEST'; //重新编译状态没变；

MVIEW_NAME               STALENESS

------------------------------ -------------------

MV_TEST                NEEDS_COMPILE

SQL> select OBJECT_NAME,STATUS,OBJECT_TYPE from dba_objects where OBJECT_NAME='MV_TEST' ;

OBJECT_NAME         STATUS          OBJECT_TYPE

-------------------- -------------------- --------------------

MV_TEST          VALID          TABLE

MV_TEST          INVALID          MATERIALIZED VIEW

显示物化视图的状态INVALID

2.5 修改源表的结构跟物化视图一致

SQL>  ALTER TABLE SCOTT.EMP RENAME COLUMN COMMS TO COMM; //修改源表的结构

SQL> SELECT mview_name,staleness FROM DBA_MVIEWS WHERE MVIEW_NAME='MV_TEST'; //需要编译

MVIEW_NAME               STALENESS

------------------------------ -------------------

MV_TEST                NEEDS_COMPILE

SQL>  ALTER MATERIALIZED VIEW SCOTT.MV_TEST COMPILE;  //进行重新编译

Materialized view altered.

SQL> SELECT mview_name,staleness FROM DBA_MVIEWS WHERE MVIEW_NAME='MV_TEST'; //状态变成STALE

MVIEW_NAME               STALENESS

------------------------------ -------------------

MV_TEST                STALE

SQL> select OBJECT_NAME,STATUS,OBJECT_TYPE from dba_objects where OBJECT_NAME='MV_TEST' ;  //状态变成VALID

OBJECT_NAME         STATUS          OBJECT_TYPE

-------------------- -------------------- --------------------

MV_TEST          VALID          TABLE

MV_TEST          VALID          MATERIALIZED VIEW

总结：当物化视图的源表重新编译了，如果重建后的表结构没有发现变化，那么运行脚本ALTER MATERIALIZED VIEW MV_NAME COMPILE后物化视图的状态就会刷新成有效的；

但是如果表的结构发生了变化，那么需要重新修改物化视图的脚本，相应的物化视图才能有效,dba_objects显示出来的状态才是VALID的状态；

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本文作者：JOHN QQ：1916066696 (请备注数据库)

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