SQL> -- Create the cluster...
SQL> CREATE CLUSTER emp_dept_cluster (
  2    deptno NUMBER);
Cluster created.

SQL> -- Create the cluster index...
SQL> CREATE INDEX emp_dept_cluster_index ON CLUSTER emp_dept_cluster;
Index created.

SQL> -- Create tables within the cluster...
SQL> CREATE TABLE emp (
  2    empid  NUMBER,
  3    name      VARCHAR2(30),
  4    deptno NUMBER)
  5    CLUSTER emp_dept_cluster(deptno);
Table created.
SQL> CREATE TABLE dept (
  2    deptno NUMBER,
  3    name      VARCHAR2(30))
  4    CLUSTER emp_dept_cluster(deptno);
Table created.

SQL> -- Insert test data...
SQL> INSERT INTO dept VALUES (1, 'Depta');
1 row created.
SQL> INSERT INTO emp  VALUES (1, 'Me',  1);
1 row created.
SQL> INSERT INTO emp  VALUES (2, 'You', 1);
1 row created.

SQL> -- Cluster tables share rowid's...
SQL> SELECT ROWID, empid FROM emp;
ROWID                   EMPID
------------------ ----------
AAAEDbAABAAAJZQAAA          1
AAAEDbAABAAAJZQAAB          2

SQL> SELECT ROWID, deptno FROM dept;
ROWID                  DEPTNO
------------------ ----------
AAAEDbAABAAAJZQAAA          1