title: MySQL Integer 0 vs NULL
body: <p>When using integer columns is it better to have <code>0</code> or <code>NULL</code> to indicate no value. </p>
  
  <p>For example, if a table had a <code>parent_id</code> field and a particular entry had no parent, would you use <code>0</code> or <code>NULL</code>?</p>
  
  <p>I have in the past always used <code>0</code>, because I come from a Java world were (prior to 1.5) integers always had to have a value. </p>
  
  <p>I am asking mainly in relation to performance, I am not too worried about which is the "more correct" option.</p>