Update Mysql table row
You need a condition() so that it knows which record to update.  When you don't give a condition, it just doesn't update anything.  More Info on db_update()

The following says, "Update firstname to formvalue, lastname to formvalue WHERE the last name as stored in database is 'Bolli'".  To avoid conflicts, your table should have a field that contains a unique value for each entry, such as an auto-increment primary key.  That way, you can say "UPDATE ... WHERE id = unique_id".

$update_zoho = db_update('zoho')
  -&gt;fields(array(
     //'title' =&gt; $form_state['values']['title'],
     'firstname' =&gt; $form_state['values']['firstname'],
     'lastname' =&gt; $form_state['values']['lastname'],
  ))
  -&gt;condition('lastname', 'Bolli', '=')
  -&gt;execute();