title: Change column value when matching condition
body: <p>I need to replace a <code>NULL</code> value in a column only when other conditions are matched.</p>
  
  <pre><code>Columns: Parent, Child, flag01, lag02
  </code></pre>
  
  <p>Parent columns has many <code>NULL</code> values, but I want to replace the <code>null</code> values only when <code>flag01</code> and <code>flag02</code> is "ok".</p>
  
  <p>If <code>flag01</code> and <code>flag02</code> are both "<code>Ok</code>" and Parent is NULL, replace to 'CT_00000'. Else, keep the original value (when NOT NULL).</p>