title: codeigniter adding the IS NULL in the find_in_set
body: <p>while generating the query through <strong>codeigniter</strong> framework</p>
  
  <pre><code>$this-&gt;db-&gt;select('id,memo,sent_to,sent_by,read_by,date')-&gt;from('memos')
      -&gt;where("FIND_IN_SET('1',`sent_to`)")-&gt;order_by('`id`','DESC')-&gt;get();
  </code></pre>
  
  <p>i got an error of adding <strong>IS NULL</strong> in the query automatically</p>
  
  <p>it produce </p>
  
  <pre><code>SELECT `id`, `memo`, `sent_to`, `sent_by`, `read_by`, `date` FROM `memos` 
  WHERE FIND_IN_SET('1',`sent_to`) IS NULL ORDER BY `id` DESC 
  </code></pre>
  
  <p>instead of </p>
  
  <pre><code>SELECT `id`, `memo`, `sent_to`, `sent_by`, `read_by`, `date` FROM `memos` 
  WHERE FIND_IN_SET('1',`sent_to`) ORDER BY `id` DESC
  </code></pre>