SQL> CREATE TABLE dept_master
  2  AS SELECT * FROM scott.dept;

Table created.

SQL> CREATE TABLE emp_detail1
  2  (empno NUMBER, deptno NUMBER);

Table created.

SQL> CREATE TABLE emp_detail2
  2  (ename VARCHAR2(32), deptno NUMBER);

Table created.

SQL> ALTER TABLE dept_master
  2  ADD CONSTRAINT empm_deptno_pk PRIMARY KEY(deptno);

Table altered.

SQL> ALTER TABLE emp_detail1
  2  ADD CONSTRAINT empd_deptno_fk FOREIGN KEY(deptno)
  3  REFERENCES dept_master(deptno);

Table altered.

SQL> ed
Wrote file afiedt.buf

  1  ALTER TABLE emp_detail2
  2  ADD CONSTRAINT empd2_deptno_fk FOREIGN KEY(deptno)
  3* REFERENCES dept_master(deptno)
SQL> /

Table altered.