title: Can someone explain me what is the difference between union All and join in oracle SQL
body: <p>I am searching for this question since last 2 days what is the difference between UNION and JOIN. Specifically UNION ALL and Natural JOIN.
  So I have 2 queries here 
  first one is </p>
  
  <pre><code>CREATE OR REPLACE VIEW VU_m1 AS 
  SELECT department_id,manager_id FROM employees 
  NATURAL JOIN departments ;
  SELECT * FROM vu_m1;
  </code></pre>
  
  <p>and the second one is </p>
  
  <pre><code>CREATE OR REPLACE VIEW VU_m2 AS 
  SELECT department_id,manager_id FROM employees 
  UNION ALL
  SELECT department_id,manager_id FROM departments; 
  SELECT * FROM vu_m2;
  </code></pre>
  
  <p>The result from both the query is exactly same.
  So now what is the difference between UNION ALL and Natural JOIN</p>
  
  <p>Details:
  I am using Oracle 11gR2 working on Sample HR database.</p>