问题描述：给表创建外键报错ORA-00906，具体过程如下：

数据库：oracle 11.2.0.464位

scott@ORCL2022-10-18 19:10:40> selectindex_name,table_name,tablespace_name,status,last_analyzed from user_indexes;

INDEX_NAME TABLE_NAME TABLESPACE_NAME STATUS LAST_ANALYZED

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

PK_EMP EMP USERS VALID 2022-10-11 22:00:04

PK_DEPT DEPT USERS VALID 2022-10-11 22:00:04

scott@ORCL2022-10-18 19:10:48> select * from app1_emp;

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO

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

7369 SMITH CLERK 7902 1980-12-1700:00:00 800 20

7499 ALLEN SALESMAN 7698 1981-02-20 00:00:00 1600 300 30

7521 WARD SALESMAN 7698 1981-02-22 00:00:00 1250 500 30

7566 JONES MANAGER 7839 1981-04-02 00:00:00 2975 20

7654 MARTIN SALESMAN 7698 1981-09-28 00:00:00 1250 1400 30

7698 BLAKE MANAGER 7839 1981-05-01 00:00:00 2850 30

7782 CLARK MANAGER 7839 1981-06-09 00:00:00 2450 10

7788 SCOTT ANALYST 7566 1987-04-19 00:00:00 3000 20

7839 KING PRESIDENT 1981-11-17 00:00:00 5000 10

7844 TURNER SALESMAN 7698 1981-09-08 00:00:00 1500 0 30

7876 ADAMS CLERK 7788 1987-05-23 00:00:00 1100 20

7900 JAMES CLERK 7698 1981-12-03 00:00:00 950 30

7902 FORD ANALYST 7566 1981-12-03 00:00:00 3000 20

7934 MILLER CLERK 7782 1982-01-23 00:00:00 1300 10

14 rowsselected.

scott@ORCL2022-10-18 19:17:45> alter table app2_dept add constraint PK_Test_ID primarykey(deptno);

scott@ORCL2022-10-18 19:51:22> alter table app1_emp add constraint fk_app1_deptnoforeign key references app2_dept(deptno);

altertable app1_emp add constraint fk_app1_deptno foreign key referencesapp2_dept(deptno)

*

ERROR atline 1:

ORA-00906:missing left parenthesis

scott@ORCL2022-10-18 19:53:27> alter table app1_emp add constraint fk_app1_deptnoforeign key (deptno) references app2_dept(deptno);

Tablealtered.

总结：创建语句不正确导致，修改后成功创建外键.