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•STALE - Materialized view is out of date because one or more of its masters has changed.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 was FRESH before it became STALE, 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. An ALTER MATERIALIZED VIEW...COMPILE statement 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；
物化视图定义不当引发Oracle性能问题
Oracle物化视图测试
Oracle【定期刷新】的【基于连接】的物化视图
Oracle物化视图创建报ORA-00942错误解决
Oracle 存储过程刷新物化视图
Oracle物化视图的使用
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