title: listing unique sellers and buyers
body: <p>I have these tables </p>
  
  <pre><code>Customer (Customer_ID(PK), Joined_date, FirstName, LastName, Location) 
  Seller (Seller_ID, Customer_ID(Fk)) and Buyer(Buyer_ID, Customer_ID(FK))
  </code></pre>
  
  <p>I need to show only those buyers and sellers who have joined after 1st jan 2016 and that person should not be listed twice who sold an item and also bought an item.</p>
  
  <pre><code>SELECT * FROM 
  (
      SELECT BUYER_FirstName, BUYER_LastName, SELLER_ID 
      FROM BUYER AS BUY 
      UNION 
      SELECT SELLER_FirstNAME,Seller_LastName, BUYER_ID 
      FROM SELLER AS SELL
  ) WHERE JOINED_DATE &gt; TO_DATE('01-01-2016', 'MM-DD-YYYY') 
  ORDER BY JOINED_DATE;
  </code></pre>
  
  <p>am i on the right track? actually i had to run these queries conceptually based on ER Diagram.</p>