一般来说，如何防止PHP中的Mysql_fetch_assoc错误？ [重复]

Question

Possible Duplicate:
Warning: mysql_fetch_array() expects parameter 1 to be resource, boolean given in problema con el wile

When I execute login form , I'll encounter with the following error:

Warning: mysql_fetch_assoc() expects parameter 1 to be resource, boolean given in C:\xampp\htdocs\login\check.php on line 22

  <?php

  include_once ("function.php");

  $username = $_POST['tfuser'] ;
  $password = $_POST['tfpass'] ;

  if (isset($username) && isset($password)){

    $link = mysql_connect('localhost','root','') or die ('error in connecting to db');
    mysql_select_db('login',$link) or die ('error select db');

    $sql = "select from * from administration 
    where username='$username' and password='$password'";

    $result = mysql_query($sql,$link);

    if (mysql_fetch_assoc($result)){
         //login to panel 
         redirect("panel.php");
    } else {
        //back to login page
    }

  } else {
      //back to login page
      redirect("index.php");
  }

  ?>

And now how can I prevent this error display and prevent Mysql_fetch_assoc error ?

Answer 1

Please read about SQL Injections.

You are receiving the following error because the execution of your SQL statement failed.

Warning: mysql_fetch_assoc() expects parameter 1 to be resource, boolean given in C:\xampp\htdocs\login\check.php on line 22

Your SQL query in:

$result = mysql_query($sql,$link);

returns FALSE. That is why when you use mysql_fetch_assoc() it returns a warning.

To fix this, ensure that your $result contains a mysql resource. One way you can do this is to stop script execution in case of a failed SQL query. You can do this:

$result = mysql_query($sql,$link) OR die(mysql_error());

That will show you why your SQL execution failed.