title: What is the usage of USING() function in mysql?
body: <p>I have 2 tables which I want to join, and I can achieve it by 2 ways:</p>
  <p><em>Customers</em>:</p>
  <pre><code>+------------+--------------------+--------------------+--------------+
  | CustomerID | Name               | Address            | City         |
  +------------+--------------------+--------------------+--------------+
  |          1 | Julie Smith        | 25 Oak Street      | Airport West |
  |          2 | Alan Wong          | 1/47 Haines Avenue | Box Hill     |
  |          3 | Michelle Arthur    | 357 North Road     | Yarraville   |
  |          4 | Geogrge Napolitano | 177 Melbourne Road | Coburg       |
  +------------+--------------------+--------------------+--------------+
  </code></pre>
  <p><em>Orders</em>:</p>
  <pre><code>+---------+------------+--------+------------+
  | OrderID | CustomerID | Amount | Date       |
  +---------+------------+--------+------------+
  |       1 |          3 |  69.98 | 2019-04-02 |
  |       2 |          1 |  49.99 | 2019-04-15 |
  |       3 |          2 |  74.99 | 2019-05-19 |
  |       4 |          3 |  24.99 | 2019-05-01 |
  +---------+------------+--------+------------+
  </code></pre>
  <p>Now I would like to select only those customers, that has <em>no</em> order placed (<code>OrderID == null</code>). That is only the <code>Geogrge Napolitano</code>. So I can use 2 ways:</p>
  <pre><code>mysql&gt; select Customers.CustomerID, Customers.Name
      -&gt; from Customers left join Orders 
      -&gt; on Customers.CustomerID = Orders.CustomerID
      -&gt; where Orders.OrderID is null;
  </code></pre>
  <p>or</p>
  <pre><code>mysql&gt; select Customers.CustomerID, Customers.Name
      -&gt; from Customers left join Orders
      -&gt; using(CustomerID)
      -&gt; where Orders.OrderID is null;
  </code></pre>
  <p>Now for me. It seems that <code>=</code> in first case (<code>Customers.CustomerID = Orders.CustomerID</code>), is <em>exactly</em> the same as <code>USING()</code> that Id. But is it always that case? In what other cases I can use the mysql function <code>USING()</code> ?</p>