title: MySQL query does not return needed result. Customers who does not have any orders, does not show
body: <p>Im still doing my SQL training. So I have two tables CUSTOMERS and ORDERS( foreign key table). Now I need to get all customers without any ORDERS. Here is my query</p>
  
  <pre><code>select LASTNAME, FIRSTNAME 
    from CUSTOMERS 
    WHERE CUSTOMERS.ID NOT IN 
        (select ID_CUSTOMER from ORDERS);
  
  +-----------+--------------+------+-----+---------+-------+
  | Field     | Type         | Null | Key | Default | Extra |
  +-----------+--------------+------+-----+---------+-------+
  | ID        | int(11)      | NO   | PRI | NULL    |       |
  | FIRSTNAME | varchar(50)  | YES  |     | NULL    |       |
  | LASTNAME  | varchar(50)  | YES  |     | NULL    |       |
  | ADDRESS   | varchar(100) | YES  |     | NULL    |       |
  +-----------+--------------+------+-----+---------+-------+
  
  
  +---------------+--------------+------+-----+---------+-------+
  | Field         | Type         | Null | Key | Default | Extra |
  +---------------+--------------+------+-----+---------+-------+
  | ID            | int(11)      | NO   | PRI | NULL    |       |
  | PRODUCT_NAME  | varchar(100) | YES  |     | NULL    |       |
  | PRODUCT_PRICE | double(10,4) | YES  |     | NULL    |       |
  | DATE_ORDER    | date         | YES  |     | NULL    |       |
  | ID_CUSTOMER   | int(11)      | YES  |     | NULL    |       |
  | AMOUNT        | int(11)      | YES  |     | NULL    |       |
  +---------------+--------------+------+-----+---------+-------+
  </code></pre>
  
  <p>But I do recieve Empty set (0,00 sec)/ But Im sure about that those are present;</p>