mysql_error() not displaying an error

Question

I am trying to debug my code but mysql_error() isn't displaying anything. I know there is something wrong, because when I write

or die("ERROR");

It displays ERROR. So the problem must be with that line of code. When I write

or die(mysql_error());

It shows up blank. Here is my code for the line that I think has the error:

while ($rows = mysql_fetch_array($sql6) or die(mysql_error())) {

Now here is the full code block:

$sql6 = mysql_query("SELECT * FROM replies WHERE thread_id = $thread_id");
    $numRows = mysql_num_rows($sql6);
    $replies = '';
    if ($numRows < 1) {
        $replies =  "There are no replies yet, you can make the first!";
    } else {
        while ($rows = mysql_fetch_array($sql6) or die(mysql_error())) {
            $reply_content = $rows['5'];
            $reply_username = $rows['7'];
            $reply_date = $rows['8'];
            $reply_author_id = $rows['4'];

            $sql9 = mysql_query("SELECT * FROM users WHERE id = '$reply_author_id'");
            $numRows = mysql_num_rows($sql9); 
            if ($numRows < 1) {
                while ($rows = mysql_fetch_array($sql9)) {
                    $reply_user_fn = $rows['first_name'];
                    $reply_user_ln = $rows['last_name'];
                    $reply_user_id = $rows['id'];
                    $reply_user_pp = $rows['profile_pic'];
                    $reply_user_lvl = $rows['user_level'];
                    $reply_user_threads = $rows['threads'];
                    $reply_user_email = $rows['email'];

                    $replies .= '<tr><td valign="top" style="border: 1px solid black;">';
                    $replies .= '<div class="reply" style="min-height: 125px;"';
                    $replies .= '<h2>Re: ' . $thread_title . '</h2><br />';
                    $replies .= '<em>by: ' . $reply_username . ' - ' . $reply_date . '</em><hr />';
                    $replies .= $reply_content;
                    $replies .= '</div></td>';
                    $replies .= '<td valign="top" width="200" align="center" style="border: 1px solid black;"';
                    $replies .= '<img src="userdata/profile_pics/' . $reply_user_pp . '" width="80" height="80"><br />';
                    $replies .= '<a href="profile.php?u=' .$reply_username . '" style="color: black;">'. $reply_username .'</a><br />';
                    $replies .= '<a href="profile.php?u=' .$reply_username . '" style="color: black;">' . $reply_user_fn.' ' .$reply_user_ln . '</a><br />';
                    $replies .= 'Threads: ' . $reply_user_threads . ' <br />Level: '. $reply_user_lvl .'<br />Sign up date: ' . $reply_user_email/*PUT SIGNUP DATE*/ .'';
                    $replies .= '<input type="button" name="addfriend" value="Add Friend">';
                    $replies .= '</td>';
                    }
                }
            }
        }

What am I doing wrong and why won't PHP display the mysql error? Thanks

Solution 1

Do not put or die() inside of a loop condition. The loop condition becoming false is what signals the loop to end, and that will also trigger die() every time your loop completes.

mysql_fetch_row() returns false when there are no more rows this is what is triggering your die() statement despite there being no error.

Solution 2

You can use a try..catch block to understand why your code is not working correctly, like this:

try {
  while ($rows = mysql_fetch_array($sql6)) {
    // your code ..
  }
} catch (Exception $e) {
  echo $e->getMessage();
  echo "---";
  echo mysql_error();
}

Note that, as you say or die is getting executed, which means that there is an error in your code somewhere, and not a mysql error. And, therefore, the above code will capture that exception and display it for you. Also, it will display any mysql_error, if it has occurred until that point for reference, so that you can compare the two strings.