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SELECT e.employee_id, e.last_name, d.location_id
  FROM employees e JOIN departments d
 USING (department_id); 

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SELECT department_id, department_name, location_id, city 
  FROM departments NATURAL JOIN locations;

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SELECT worker.last_name || ' works for ' || manager.last_name worker_works_for_manager
  FROM employees worker, employees manager
 WHERE worker.manager_id = manager.employee_id;

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SELECT e.last_name, e.department_id, d.department_name
  FROM employees e FULL OUTER JOIN departments d
    ON (e.department_id = d.department_id);   

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SELECT e.last_name, e.department_id, d.department_name
  FROM employees e RIGHT OUTER JOIN departments d
    ON (e.department_id = d.department_id);    

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SELECT e.last_name, e.department_id, d.department_name
  FROM employees e LEFT OUTER JOIN departments d
    ON (e.department_id = d.department_id);

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SELECT e.last_name, e.salary, j.grade
  FROM employees e, job_grades j
 WHERE e.salary BETWEEN j.lowest_sal AND j.highest_sal;

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-- Joining more than two tables with JOIN and ON keywords
SELECT e.last_name, d.department_name, l.city
  FROM employees e JOIN departments d
    ON (e.department_id = d.department_id)
  JOIN locations l
    ON (d.location_id = l.location_id);

-- Joining more than two tables with equal (=) operator
SELECT e.last_name, d.department_name, l.city
  FROM employees e, departments d, locations l

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-- Inner Join with the ON Clause
SELECT e.employee_id, e.last_name, e.department_id, d.department_id, d.location_id
  FROM employees e JOIN departments d
    ON (e.department_id = d.department_id);

-- Inner Join with the Equal (=) Operator
SELECT e.employee_id, e.last_name, e.department_id, d.department_id, d.location_id
  FROM employees e, departments d
 WHERE e.department_id = d.department_id;

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-- Cartesian product
SELECT employee_id, first_name || last_name full_name, job_id, department_name
  FROM employees, departments;
  
-- Cartesian product with CROSS JOIN syntax   
SELECT last_name, department_name
  FROM employees CROSS JOIN departments;