title: Reverse effect of Join in mysql
body: <p>I'm developing a system and creating invoices. I want the record where no invoice has been created.</p>
  
  <p>I'm trying to write a MySQL query, where I need the records whch can not be joined with another table. In other words, the records that do not have a linked record in the other table.</p>
  
  <p>I tried the following query </p>
  
  <pre><code>SELECT exports.id as e_id,export_invoices.id as i_id 
  FROM exports 
  LEFT JOIN export_invoices ON export_invoices.export_id = exports.id
  </code></pre>
  
  <p>and got this result: </p>
  
  <p><img src="https://i.stack.imgur.com/YHggP.png" alt="enter image description here"></p>
  
  <p>Which gives all value and also the record of which invoice is not created with NULL value (I want to have that [e_id->2 from result]). I just want to extract that null value record's master id.</p>