oracle: OCA-047-题解与实验(2）

题目：



逐条分析吧：

A：正确，USER_SYNONYMS describes the private synonyms (synonyms owned by the current user). Its columns (except for OWNER) are the same as those in ALL_SYNONYMS.通过他的描述即可判断。在数据库里同义词就相当于表的别名的功能，用一个别名来代表一个表。如：

SQL> create or replace synonym syn1 for jobs;

Synonym created

SQL> select * from user_synonyms;

SYNONYM_NAME  TABLE_OWNER  TABLE_NAME  DB_LINK
------------- ------------ ----------- -------------
SYN1          HR           JOBS

SQL> desc user_synonyms;
Name         Type          Nullable Default Comments
------------ ------------- -------- ------- ---------------------------------------------
SYNONYM_NAME VARCHAR2(30)                   Name of the synonym
TABLE_OWNER  VARCHAR2(30)  Y                Owner of the object referenced by the synonym
TABLE_NAME   VARCHAR2(30)                   Name of the object referenced by the synonym
DB_LINK      VARCHAR2(128) Y                Database link referenced in a remote synonym

SQL> select * from syn1;

JOB_ID     JOB_TITLE                           MIN_SALARY MAX_SALARY
---------- ----------------------------------- ---------- ----------
AD_PRES    President                                20080      40000
AD_VP      Administration Vice President            15000      30000
AD_ASST    Administration Assistant                  3000       6000
FI_MGR     Finance Manager                           8200      16000

创建synonym的语句格式是：

CREATE [ OR REPLACE ] [ PUBLIC ] SYNONYM
[ schema. ] synonym
FOR [ schema. ] object [ @ dblink ] ;

B：错误，应该是sys用户，而不是system用户；

SQL> select count(*) from dba_tables where owner='SYSTEM';

COUNT(*)
----------
156

SQL> select count(*) from dba_tables where owner='SYS';

COUNT(*)
----------
954

SQL>

C：错误，动态性能视图并不是全部都开放给所有用户；

D：错误，不是created by the user only 而是owned by the user only，原文档描述是：USER_OBJECTS describes all objects owned by the current user. Its columns are the same as those in ALL_OBJECTS；

E：正确，DICTIONARY contains descriptions of data dictionary tables and views. 用户查询时只会列出用户可以访问的数据字典行；