Just dropping quickly here, and wanting to share a little and yet important part of software development, in web or in any platform.

I believe it is always nice to have a property in your object (or class) to hold the latest error encountered or latest command executed. Sort of like this

class test1
{
  var $last_error;
  var $last_cmd;
  // some other properties here
  function test1()
  {
    // other codes here
  }
  /**
   * the "why" for this class
   */
  function execute()
  {
    $command = $this->get_command();
    $this->last_cmd = $command;
    system($command, $res);
    if ($res)
    {
      $this->last_error = $res;
      return false;
    }
    return true;
  }
}

I realize the need for these two properties when I was debugging the CMS I was working on. It involved GraphicsMagick to process resizing, cropping and sharpening image, and executed thru PHP exec or system functions. I forgot why I arrived at using exec over the other. What I did was include these two properties in the log thru a logger method of another class in the system, which indeed, helped me get back to my sanity .

Update only columns that has changed.

Its tedious to compare old column values against the new being submitted before adding the column in the query statement. But, most of the articles I read says its the most efficient.

+---------------+--------------------------+-----------------+
| username      | email                    | lastip          |
+---------------+--------------------------+-----------------+
| admin         | admin@google.com.ph      | 127.0.0.1       |
+---------------+--------------------------+-----------------+

In this example, current $row["email"] is compared to request $email value

/* repeat this test in every column in your table */
if ($row["email"] != $email)
{
  $columns[] = "email = '$email'";
}
/* constructed sql statement would be */
$sql = "update customer set email = '$email' where username = 'admin'";

Another advantage following this convention is when there are multiple users accessing the same row. Though it sounds impossible that same row is updated at an exact same time, unless your site tops google on ranking. And even so, your SQL operation would have saved a little less resource than usual.