title: How to find orders from repeat/old customers using sql query?
body: <p>I am using mysql.</p>
  
  <p>I have <code>orders</code> table with column <code>customer_id, order_id, order_date(datetime)</code> now I want to find all orders on Dec 20, 2013, which are from repeat customers( not new customer, i.e. customers has placed some order before as well) in a single query.</p>
  
  <p><code>Orders</code> table has other typical columns as well not mentioned here. Let me know I can provide more data.</p>
  
  <p>UPDATE: Can we do it without subquery? If yes how? (Just curious) </p>