视图insert,delete,update对基表的影响（视图初识）

视图进行insert,delete,update对基表的影响（视图初识）

 

一、问题：解决官档部分词语不理解

官档中oracle concepts=>partitions,views有这样一段话不理解。

All operations performed on a view actually affect the base tables.（通过实验1有了初步了解）

 

二、实验解决问题

 

1、 对视图t_view进行DML操作，查看基表t数据

 

实验表明：对视图T_VIEW进行DML直接影响基表T的数据

doudou@TEST> insert into t_view values (11,'兜兜+小鱼');

1 row created.

doudou@TEST> commit;

Commit complete.

doudou@TEST> update t_view set id=110 where id=11;

1 row updated.

doudou@TEST> commit;

Commit complete.

doudou@TEST> select * from t_view where id=110;

        ID NAME

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

       110 兜兜+小鱼

doudou@TEST> select * from t where id=110;

        ID NAME

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

       110 兜兜+小鱼

doudou@TEST> delete t_view where rownum<5;

4 rows deleted.

doudou@TEST> commit;

Commit complete.

doudou@TEST> select count(*) from t_view;

  COUNT(*)

----------

         7

doudou@TEST> select count(*) from t;

  COUNT(*)

----------

         7

 

2、 对基表t进行DML，查看视图t_view结果

 

实验表明：对基表T进行DML，数据库自动维护更新视图

doudou@TEST> insert into t values (100,'兜兜+兜兜');

1 row created.

doudou@TEST> commit;

Commit complete.

doudou@TEST> select * from t_view where id=100;

        ID NAME

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

       100 兜兜+兜兜

doudou@TEST> update t set name='兜兜+update' where id=100;

1 row updated.

doudou@TEST> commit;

Commit complete.

doudou@TEST> select * from t_view where id=100;

        ID NAME

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

       100 兜兜+update

doudou@TEST> delete t where id=100;

1 row deleted.

doudou@TEST> commit;

Commit complete.

doudou@TEST> select * from t_view where id=100;

no rows selected

 

3、 drop view 查看基表t的影响

 

实验表明：drop view对基表t没有影响

doudou@TEST> select count(*) from t;

  COUNT(*)

----------

         7

doudou@TEST> select count(*) from t_view;

  COUNT(*)

----------

         7

doudou@TEST> drop view t_view;

View dropped.

doudou@TEST> select count(*) from t;

  COUNT(*)

----------

         7

doudou@TEST> select count(*) from t_view;

select count(*) from t_view

                     *

ERROR at line 1:

ORA-00942: table or view does not exist

 

4、 drop 基表t查看对视图t_view影响

 

实验表明：drop base tables 对view 有影响，视图的数据没了，但是视图在数据字典中的定义还是存在的。

删除基表对视图有影响，视图报错了，因为视图不包含数据，数据都来源于基表，所以基表没有了，视图也报错了，视图虽然不存储数据，但是会把定义保存在数据字典中。所以user_views还是可以看到视图记录

 

doudou@TEST> create view t_view as select * from t;

View created.

doudou@TEST> select count(*) from t;

  COUNT(*)

----------

         7

doudou@TEST> select count(*) from t_view;

  COUNT(*)

----------

         7

doudou@TEST> drop table t ;

Table dropped.

doudou@TEST> select count(*) from t;

select count(*) from t

                     *

ERROR at line 1:

ORA-00942: table or view does not exist

doudou@TEST> select count(*) from t_view;

select count(*) from t_view

                     *

ERROR at line 1:

ORA-04063: view "DOUDOU.T_VIEW" has errors

doudou@TEST> desc t_view;

ERROR:

ORA-24372: invalid object for describe

doudou@TEST> select view_name from user_views;

 

VIEW_NAME

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

T_VIEW --（数据字典中还是存在视图的）

T1_VIEW

TEST_VIEW

【基表T被删除，视图T_VIEW没有删除，查看视图T_VIEW会报相应错误：ORA-04063或是ORA-24372】

 

拓展：看到oracle报错，先看看oracle是怎么定义这个错误的，然后想想处理方法

[ora@dg-pp ~]$ oerr ora 4063

04063, 00000, "%s has errors"

// *Cause:  Attempt to execute a stored procedure or use a view that has

//          errors.  For stored procedures, the problem could be syntax errors

//          or references to other, non-existent procedures.  For views,

//          the problem could be a reference in the view's defining query to

//          a non-existent table.（视图参考表不存在）

//          Can also be a table which has references to non-existent or

//          inaccessible types.

// *Action: Fix the errors and/or create referenced objects as necessary.

 

[ora@dg-pp ~]$ oerr ora 24372

24372, 00000, "invalid object for describe"

// *Cause:  The object to be described is not valid.

//          It either has compilation or authorization errors.

// *Action: The object to be described must be valid.

 

三、总结

 

1、  视图的DML操作对基表是有影响的，视图的insert,update,delete相关的基表也会被insert,update,delete

2、  Drop视图对基表没有影响，删除基表后视图会没有数据，因为视图是不包含数据的（物化视图除外）。数据字典中还有删除基表的视图记录，就有了ORA-04063报错

 

附表

 

一、实验环境

 

建立实验表t、t1 及插入数据SQL

doudou@TEST> create table t (id number, name varchar2(40));

Table created.

doudou@TEST> begin

  2  for i in 1..10 loop

  3  insert into t values (i,'兜兜');

  4  end loop;

  5  commit;

  6  end ;

  7  /

PL/SQL procedure successfully completed.

doudou@TEST> create table t1 (id number, city_name varchar2(40));

Table created.

doudou@TEST> begin

  2  for i in 1..10 loop

  3  insert into t1 values (i,'北京');

  4  end loop;

  5  commit;

  6  end;

  7  /

PL/SQL procedure successfully completed.

 

User_updatable_columns当前用户建立视图有适当的更新权限

doudou@TEST> select table_name,column_name,updatable,insertable,deletable from user_updatable_columns where table_name in ('T','T1');

 

TABLE_NAME           COLUMN_NAME                    UPDATA INSERT DELETA

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

T                    ID                             YES    YES    YES

T                    NAME                           YES    YES    YES

T1                   ID                             YES    YES    YES

T1                   CITY_NAME                      YES    YES    YES

 

建立视图t、t1

doudou@TEST> create view t_view as select * from t;

View created.

doudou@TEST> create view t1_view as select * from t1;

View created.

 

二、知识点：

 

1、 all operations performed on a view actually affect the base tables

oracle concepts=>partions,views=>overview of views

http://docs.oracle.com/cd/E11882_01/server.112/e25789/schemaob.htm#autoId9

2、 USER_UPDATABLE_COLUMNS

USER_UPDATABLE_COLUMNS describes all columns owned by the current user that are in a join view and are updatable by the current user, subject to appropriate privileges.

http://docs.oracle.com/cd/B19306_01/server.102/b14237/statviews_2113.htm#i1593275

3、 a view is not allocated storage space,nor does a view contain data

         Oracle concepts=>partions,views=>characteristics of views

Unlike a table, a view is not allocated storage space, nor does a view contain data. Rather, a view is defined by a query that extracts or derives data from the base tables referenced by the view. Because a view is based on other objects, it requires no storage other than storage for the query that defines the view in the data dictionary.

A view has dependencies on its referenced objects, which are automatically handled by the database. For example, if you drop and re-create a base table of a view, then the database determines whether the new base table is acceptable to the view definition.

http://docs.oracle.com/cd/E11882_01/server.112/e25789/schemaob.htm#autoId9

 

4、 user_views 使用user_views视图查看视图t_view的建立语句，从而找到基表

doudou@TEST> select view_name,text from user_views;

VIEW_NAME  TEXT
---------- --------------------------------------------------------------------------------
T_VIEW     select "ID","NAME" from t
T1_VIEW    select "ID","CITY_NAME" from t1
TEST_VIEW  select a.id,a.name,b.city_name from t a, t1 b where a.id=b.id

5、 小议user_xxx,all_xxx,dba_xxx视图查看权限区别

     1、权限区别
USER_VIEWS describes the views owned by the current user.
ALL_VIEWS describes the views accessible to the current user.
DBA_VIEWS describes all views in the database.
     2、（未完待续，后续学习中还会补充）

user_views
http://docs.oracle.com/cd/E11882_01/server.112/e25513/statviews_5499.htm#REFRN26305
all_views
dba_views
http://docs.oracle.com/cd/E11882_01/server.112/e25513/statviews_2132.htm#i1593583

 

 

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