Oracle FOREIGN KEY constraint child table, parent table

CREATE TABLE Employees (
EMPLOYEE_ID Number (6),
Last_Name VARCHAR2 (+) not NULL,
Email VARCHAR2 (25),
Salary number (8,2),
commission_pct number (2,2),
Hire_date date not NULL,
...
DEPARTMENT_ID Number (4),
CONSTRAINT emp_dept_fk FOREIGN KEY (department_id)
REFERENCES departments (department_id),
CONSTRAINT emp_email_uk UNIQUE (email));

FOREIGN KEY: Specify columns in a child table at the table level
REFERENCES: Identifying columns in a parent table
On delete CASCADE: When a column in the parent table is deleted, the corresponding column in the child table is also deleted
On DELETE SET null: The corresponding column in the child table is empty

Oracle FOREIGN KEY constraint child table, parent table