title: SQL Query "like" operator error, when the field is null
body: <p>this query returns 421 records:</p>
  
  <p><img src="https://i.stack.imgur.com/zDR9o.png" alt="this query returns 421 records"></p>
  
  <p>Now when I implement the "like" operator, it returns 349 records, it is not taking into account the records with the field "invoice_number" in null:</p>
  
  <p><img src="https://i.stack.imgur.com/vrzu7.png" alt="Now when I implement the &quot;like&quot; operator, it returns 349 records, it is not taking into account the records with the field &quot;invoice_number&quot; in null"></p>