oracle: OCA-047-題解與實驗(2）

題目：

逐條分析吧：

A：正確，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.通過他的描述即可判斷。在資料庫裡同義字就相當於表的別名的功能，用一個別名來代表一個表。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      40000AD_VP      Administration Vice President            15000      30000AD_ASST    Administration Assistant                  3000       6000FI_MGR     Finance Manager                           8200      16000

建立synonym的語句格式是： 

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

B：錯誤，應該是sys使用者，而不是system使用者；

SQL> select count(*) from dba_tables where owner='SYSTEM';   COUNT(*)----------       156 SQL> select count(*) from dba_tables where owner='SYS';   COUNT(*)----------       954 SQL> 

C：錯誤，動態效能檢視並不是全部都開放給所有使用者；
D：錯誤，不是created by the user only 而是owned by the user only，原文檔描述是：USER_OBJECTS describes all objects owned by the current user. Its columns are the same as those in ALL_OBJECTS；
E：正確，DICTIONARY contains descriptions of data dictionary tables and views. 使用者查詢時只會列出使用者可以訪問的資料字典行；