title: MySQL IS NULL alternative
body: <p>I have a query that compares 2 tables:</p>
  
  <pre><code>SELECT a.id FROM a
      LEFT JOIN b
      ON a.id = b.id
      WHERE b.id IS NULL
  </code></pre>
  
  <p>Is that ok to use an alternative like that?</p>
  
  <pre><code>SELECT a.id FROM a
      LEFT JOIN b
      ON a.id = b.id
      WHERE LENGTH(b.id) = 0
  </code></pre>
  
  <p>Keeping in mind that a.id not found in b would return 'NULL'.</p>