同義詞定義
當(dāng)一個(gè)用戶想訪問(wèn)另外一個(gè)用戶的表時(shí)，
需要在表前加用戶名，總加表名不方便，
為此可以為用戶名、表名起個(gè)小名別名，
以方便訪問(wèn)，此別名就是同義詞。

創(chuàng)建同義詞
create synonym??同義詞名??for 用戶名.表名稱;

刪除同義詞
drop? synonym? syn_name;

測(cè)試實(shí)例

--沒(méi)有創(chuàng)建同義詞之前

SQL> select * from scott.emp where deptno = 10;
 
EMPNO ENAME      JOB         MGR HIREDATE          SAL      COMM DEPTNO
----- ---------- --------- ----- ----------- --------- --------- ------
 7782 CLARK      MANAGER    7839 1981-6-9      2450.00               10
 7839 KING       PRESIDENT       1981-11-17    5000.00               10
 7934 MILLER     CLERK      7782 1982-1-23     1300.00               10
 
Executed in 0.078 seconds

--創(chuàng)建同義詞

SQL> create synonym myemp for scott.emp;
 
Synonym created
 
Executed in 0.265 seconds

--使用同義詞

SQL> select * from myemp where deptno = 10;
 
EMPNO ENAME      JOB         MGR HIREDATE          SAL      COMM DEPTNO
----- ---------- --------- ----- ----------- --------- --------- ------
 7782 CLARK      MANAGER    7839 1981-6-9      2450.00               10
 7839 KING       PRESIDENT       1981-11-17    5000.00               10
 7934 MILLER     CLERK      7782 1982-1-23     1300.00               10
 
Executed in 0.047 seconds