当我们没有权限访问业务表，但是需要查看shared pool中部分sql语句的执行计划，原则上来说，查询v$sql_plan视图结合hash_value可以实现，但是因为这个是表格形式，看起来不太美观，和我们长看的执行计划有一定的出入，这里提供两个脚本，实现查看该种情况下的执行计划。
oracle 9i

[oracle@xifenfei ~]$ more get_plan.sql 
set pagesize 0
set linesize 150
set serveroutput on size 10000
col plan_table_output format a125
undefine hash_value
set verify off feedback off
var hash_value varchar2(20)
begin
  :hash_value := '&hash_value';
end;
/
insert into plan_table
      (statement_id,timestamp,operation,options,object_node,object_owner,object_name,
       optimizer,search_columns,id,parent_id,position,cost,cardinality,bytes,other_tag,
       partition_start,partition_stop,partition_id,other,distribution,
       cpu_cost,io_cost,temp_space,access_predicates,filter_predicates
      )
select distinct hash_value,sysdate,operation,options,object_node,object_owner,object_name,
       optimizer,search_columns,id,parent_id,position,cost,cardinality,bytes,other_tag,
       partition_start,partition_stop,partition_id,other,distribution,
       cpu_cost,io_cost,temp_space,access_predicates,filter_predicates
  from v$sql_plan
 where hash_value = :hash_value
/
col piece noprint
select distinct piece,sql_text from v$sqltext where hash_value = :hash_value order by piece
/
@?/rdbms/admin/utlxplp.sql
set linesize 80
set verify on feedback on pagesize 1000

oracle 10g/11g

[oracle@xifenfei ~]$ more get_plan.sql 
set pagesize 0
set linesize 150
set serveroutput on size 10000
col plan_table_output format a125
undefine hash_value
set verify off feedback off
var hash_value varchar2(20)
begin
  :hash_value := '&hash_value';
end;
/
insert into plan_table
      (statement_id,timestamp,operation,options,object_node,object_owner,object_name,
       optimizer,search_columns,id,parent_id,position,cost,cardinality,bytes,other_tag,
       partition_start,partition_stop,partition_id,other,distribution,
       cpu_cost,io_cost,temp_space,access_predicates,filter_predicates,
       plan_id,OBJECT_ALIAS,DEPTH,PROJECTION,TIME,QBLOCK_NAME
      )
select distinct hash_value,sysdate,operation,options,object_node,object_owner,object_name,
       optimizer,search_columns,id,parent_id,position,cost,cardinality,bytes,other_tag,
       partition_start,partition_stop,partition_id,other,distribution,
       cpu_cost,io_cost,temp_space,access_predicates,filter_predicates,
       :hash_value,OBJECT_ALIAS,DEPTH,PROJECTION,TIME,QBLOCK_NAME
  from v$sql_plan
 where hash_value = :hash_value
/
col piece noprint
select distinct piece,sql_text from v$sqltext where hash_value = :hash_value order by piece
/
@?/rdbms/admin/utlxplp.sql
set linesize 80
set verify on feedback on pagesize 1000

使用方法

SQL> SELECT hash_value FROM V$SQL WHERE SQL_TEXT 
  2  LIKE 'SELECT * FROM SYS.SMON_SCN_TIME';

HASH_VALUE
----------
3019898357

SQL> @get_plan.sql
Enter value for hash_value: 3019898357
SELECT * FROM SYS.SMON_SCN_TIME

-----------------------------------------------------------------------------------
| Id  | Operation         | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |               |       |       |     3 (100)|          |
|   1 |  TABLE ACCESS FULL| SMON_SCN_TIME |     1 |  1163 |     3   (0)| 00:00:01 |
-----------------------------------------------------------------------------------

补充说明
其实9i和10g/11g中得出执行计划的出入就是在plan_table表上
在9i中：plan_table表需要通过脚本创建并且授权

SQL> connect / as sysdba;
SQL> @?/rdbms/admin/utlxplan.sql;
SQL> create public synonym plan_table for plan_table; --建立同义词
SQL> grant all on plan_table to public;--授权所有用户

在10g/11g中：plan_table表系统自带，不需要创建。因为plan_table表中含有plan_id列，而得出执行计划时该列不能为空，所以上面脚本中对于10/11g数据库必须要填充plan_id值

有些朋友创建了一个非public的dblink，现在该数据库的其他用户需要去使用该dblink，在正常情况下无访问权限，需要重新建一个dblink，或者将原dblink修改为public。但是由于忘记了原dblink的目标段的密码，使得创建或者修改dblink的步骤无法进行下去。这里通过修改基表(link$)，解决该问题。

创建dblink

SQL> show user;
USER is "SYS"
SQL> create database link "xff_dblink"
  2  connect to TEST
  3  identified by "test"
  4  using '11.1.1.1:1521/mcrm';

Database link created.

SQL> select * from dba_db_links where db_link like 'XFF_DBLINK%';

OWNER DB_LINK                                     USERN HOST               CREATED
----- ------------------------------------------- ----- ------------------ --------
SYS   XFF_DBLINK.REGRESS.RDBMS.DEV.US.ORACLE.COM  TEST  11.1.1.1:1521/mcrm 29-MAR-12

SQL> select sysdate from dual@xff_dblink;

SYSDATE
---------
29-MAR-12

SQL> CONN TEST/TEST
Connected.
SQL> SELECT SYSDATE FROM DUAL@XFF_DBLINK;
SELECT SYSDATE FROM DUAL@XFF_DBLINK
                         *
ERROR at line 1:
ORA-02019: connection description for remote database not found
--该dblink不是public的，所以test用户无权访问

dblink变为public类型

SQL> CONN / AS SYSDBA
Connected.
SQL> set long 1000
SQL> select  text from dba_views where view_name='DBA_DB_LINKS';

TEXT
-------------------------------------------------------------------
select u.name, l.name, l.userid, l.host, l.ctime
from sys.link$ l, sys.user$ u
where l.owner# = u.user#
--查询出dblink相关的基表有link$和user$

SQL> desc sys.link$
 Name                          Null?    Type
 ----------------------------- -------- --------------------
 OWNER#                        NOT NULL NUMBER
 NAME                          NOT NULL VARCHAR2(128)
 CTIME                         NOT NULL DATE
 HOST                                   VARCHAR2(2000)
 USERID                                 VARCHAR2(30)
 PASSWORD                               VARCHAR2(30)
 FLAG                                   NUMBER
 AUTHUSR                                VARCHAR2(30)
 AUTHPWD                                VARCHAR2(30)
 PASSWORDX                              RAW(128)
 AUTHPWDX                               RAW(128)

SQL> select owner# from sys.link$ where name like 'XFF_DBLINK%';

    OWNER#
----------
         0
--XFF_DBLINK对应的用户标识记录在link$.owner#中

SQL> SELECT USER#,NAME FROM USER$ WHERE name in ('SYS','PUBLIC');

     USER# NAME
---------- ------------------------------
         1 PUBLIC
         0 SYS
--现link$.owner#值为0，表示该dblink所属用户为SYS，现在让该dblink变为public
--现需要让该dblink变为public，需要做的是修改link$.owner#的值为1

SQL> UPDATE LINK$ SET OWNER#=1 WHERE name like 'XFF_DBLINK%';

1 row updated.

SQL> COMMIT;

Commit complete.

--需要刷新shared_pool
SQL> ALTER SYSTEM FLUSH SHARED_POOL;

System altered.

--查看dblink所属者，已经修改为public
SQL> select owner from dba_db_links where db_link like 'XFF_DBLINK%';

OWNER
----------
PUBLIC

--测试dblink是否成功
SQL> CONN TEST/TEST
Connected.
SQL> SELECT SYSDATE FROM DUAL@XFF_DBLINK;

SYSDATE
---------
29-MAR-12