Oracle的物化视图提供了强大的功能，可以用于预先计算并保存表连接或聚集等耗时较多的操作的结果，这样，在执行查询时，就可以避免进行这些耗时的操作，而从快速的得到结果。关于物化视图相关的说明参考：
http://blog.csdn.net/tianlesoftware/article/details/4713553
http://blog.csdn.net/tianlesoftware/article/details/7719679
在我们创建物化视图失败时，Oracle给的错误信息过于简单，不能帮助我们定位具体的问题，Oracle 为此提供了dbms_mview.explain_mview过程帮助我们快速定位问题的原因。
一.EXPLAIN_MVIEW 说明
使用explain_mview过程先要建立mv_capabilities_table表，建表的脚步是$oracle_home/rdbms/admin/utlxmv.sql。（explain_mview过程是两个过程的重载，一个输出到mv_capabilities_table表，另一个以pl/sql的varray格式输出）。
SQL>@?/rdbms/admin/utlxmv.sql
Table created.
查看utlxmv.sql 脚本，可以看到mv_capabilities_tables 表的定义：
CREATETABLEMV_CAPABILITIES_TABLE
(STATEMENT_ID VARCHAR(30), --Client-supplied unique statement identifier
MVOWNER VARCHAR(30), -- NULLfor SELECT based EXPLAIN_MVIEW
MVNAME VARCHAR(30), -- NULLfor SELECT based EXPLAIN_MVIEW
CAPABILITY_NAME VARCHAR(30), -- A descriptivename of the particular
--capability:
--REWRITE
-- Can do at least full text match
-- rewrite
--REWRITE_PARTIAL_TEXT_MATCH
-- Can do at leat full and partial
-- text match rewrite
--REWRITE_GENERAL
-- Can do all forms of rewrite
-- REFRESH
-- Can do at least complete refresh
--REFRESH_FROM_LOG_AFTER_INSERT
-- Can do fast refresh from an mv log
-- or change capture table at least
-- when update operations are
-- restricted to INSERT
--REFRESH_FROM_LOG_AFTER_ANY
-- can do fast refresh from an mv log
-- or change capture table after any
-- combination of updates
-- PCT
-- Can do Enhanced Update Tracking on
-- the table named in the RELATED_NAME
-- column. EUT is needed for fast
-- refresh after partitioned
-- maintenance operations on the table
-- named in the RELATED_NAME column
-- and to do non-stale tolerated
-- rewrite when the mv is partially
-- stale with respect to the table
-- named in the RELATED_NAME column.
-- EUT can also sometimes enable fast
-- refresh of updates to the table
-- named in the RELATED_NAME column
-- when fast refresh from an mv log
-- or change capture table is not
-- possilbe.
POSSIBLE CHARACTER(1), -- T = capabilityis possible
-- F =capability is not possible
RELATED_TEXT VARCHAR(2000),-- Owner.table.column, alias name,etc.
-- related to this message. The
--specific meaning of this column
--depends on the MSGNO column. See
-- thedocumentation for
--DBMS_MVIEW.EXPLAIN_MVIEW() for details
RELATED_NUM NUMBER, -- When there is a numeric value
--associated with a row, it goes here.
-- The specific meaning of thiscolumn
--depends on the MSGNO column. See
-- thedocumentation for
--DBMS_MVIEW.EXPLAIN_MVIEW() for details
MSGNO INTEGER, -- When available, QSM message #
--explaining why not possible or more
--details when enabled.
MSGTXT VARCHAR(2000),-- Text associated with MSGNO.
SEQ NUMBER);
-- Useful in ORDERBY clause when
--selecting from this table.
二．Explain_mview 使用示例
dbms_mview.explain_mview能分析三种不同的物化视图代码，分别是：
1.定义的查询
2.一个create materialized view的语句
3.一个存在的物化视图
因为物化视图在语法有一定的限制，所以在创建物化视图之前我们可以先使用explain_mview 过程来验证一下语法上的问题。如：
SQL> execdbms_mview.explain_mview('select * from dave');
PL/SQL proceduresuccessfully completed.
--然后查看mv_capabilities_table 表：
SQL> desc mv_capabilities_table
Name
---------------------------------
STATEMENT_ID
MVOWNER
MVNAME
CAPABILITY_NAME
POSSIBLE
RELATED_TEXT
RELATED_NUM
MSGNO
MSGTXT
SEQ
SQL> selectcapability_name,possible,msgtxt from mv_capabilities_table;
CAPABILITY_NAME P MSGTXT
------------------------------ ------------------------------------------------------------------------------------
PCT N
REFRESH_COMPLETE N no primary key constraint inthe master table
--这里提示我们主表没有主键，
REFRESH_FAST N
REWRITE N
PCT_TABLE N Oracle error: seeRELATED_NUM and RELATED_TEXT for details
REFRESH_FAST_AFTER_INSERT N the detail table does not have amaterialized view log
REFRESH_FAST_AFTER_ONETAB_DML N see the reason why REFRESH_FAST_AFTER_INSERTis disabled
REFRESH_FAST_AFTER_ANY_DML N see the reason whyREFRESH_FAST_AFTER_ONETAB_DML is disabled
REFRESH_FAST_PCT N PCT is not possible on any ofthe detail tables in the materialized view
REWRITE_FULL_TEXT_MATCH NOracle error: see RELATED_NUM and RELATED_TEXT for details
REWRITE_PARTIAL_TEXT_MATCH N materialized view cannot support anytype of query rewrite
REWRITE_GENERAL N materialized view cannotsupport any type of query rewrite
REWRITE_PCT N general rewrite is notpossible or PCT is not possible on any of the detail tables
PCT_TABLE_REWRITE N Oracle error: see RELATED_NUMand RELATED_TEXT for details
--这里会显示所有不符合的地方。
SQL> create materialized view mv_daverefresh fast on demand as select * from dave;
create materialized view mv_dave refreshfast on demand as select * from dave
*
ERROR at line 1:
ORA-12014: 表 'DAVE' 不包含主键约束条件
--如果我们直接使用上面的语句，就会出现没有主键的错误。
我们创建一个新的物化视图，然后使用explain_mview 来验证：
SQL> create table anqing as select *from all_users;
Table created.
SQL> create materialized view mv_daverefresh force on demand as select * from anqing;
Materialized view created.
SQL> exec dbms_mview.explain_mview('mv_dave');
PL/SQL procedure successfully completed.
SQL> selectcapability_name,possible,msgtxt from mv_capabilities_table wheremvname='MV_DAVE';
CAPABILITY_NAME P MSGTXT
------------------------------ -----------------------------------------------------------------------------------
PCT N
REFRESH_COMPLETE Y
REFRESH_FAST N
REWRITE N
PCT_TABLE N Oracle error: seeRELATED_NUM and RELATED_TEXT for details
REFRESH_FAST_AFTER_INSERT N does not meet the requirements of aprimary key mv
REFRESH_FAST_AFTER_ONETAB_DML N see the reason whyREFRESH_FAST_AFTER_INSERT is disabled
REFRESH_FAST_AFTER_ANY_DML N see the reason whyREFRESH_FAST_AFTER_ONETAB_DML is disabled
REFRESH_FAST_PCT N PCT is not possible on any ofthe detail tables in the materialized view
REWRITE_FULL_TEXT_MATCH N Oracle error: see RELATED_NUM andRELATED_TEXT for details
REWRITE_FULL_TEXT_MATCH N query rewrite is disabled on thematerialized view
REWRITE_PARTIAL_TEXT_MATCH N materialized view cannot support anytype of query rewrite
REWRITE_PARTIAL_TEXT_MATCH N query rewrite is disabled on thematerialized view
REWRITE_GENERAL N materialized view cannotsupport any type of query rewrite
REWRITE_GENERAL N query rewrite is disabled onthe materialized view
REWRITE_PCT N general rewrite is not possible or PCT isnot possible on any of the detail tables
PCT_TABLE_REWRITE N Oracle error: see RELATED_NUMand RELATED_TEXT for details
17 rows selected.
--这里就ok了。
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