CREATE TABLE EMPLOYEE_REGISTER
(
 EMP_ID  NUMBER PRIMARY KEY,
 EMP_SAL FLOAT
);


CREATE TABLE EMPLOYEE_DEPT
(
 DEPT_ID NUMBER PRIMARY KEY,
 DEPT_NAME    VARCHAR(100)
);


CREATE TABLE EMPLOYEE_DEPT_DETAILS
(
 EMP_DETAILS_ID  NUMBER PRIMARY KEY,
 EMP_EMP_ID   NUMBER NOT NULL,
 EMP_DEPT_ID  NUMBER NOT NULL,	 
 FOREIGN KEY(EMP_EMP_ID)REFERENCES EMPLOYEE_REGISTER(EMP_ID),
 FOREIGN KEY(EMP_DEPT_ID)REFERENCES EMPLOYEE_DEPT(DEPT_ID)
 );
 

 INSERT INTO EMPLOYEE_REGISTER VALUES (1,1000);
 INSERT INTO EMPLOYEE_DEPT VALUES (1,'IT');
 INSERT INTO EMPLOYEE_DEPT_DETAILS VALUES (1,1,1);

COMMIT;
 
DROP TABLE EMPLOYEE_REGISTER;
ORA-02449: unique/primary keys in table referenced by foreign keys

DELETE FROM EMPLOYEE_REGISTER CASCADE CONSTRAINTS Table Dropped.