Using mysql_real_escape_string() around each variable prevents SQL Injection

Using mysql_real_escape_string() around each variable prevents SQL Injection. This example demonstrates the "best practice" method for querying a database, independent of the Magic Quotes setting.

You can also use mysql_real_escape_string() to filter the smart quotes.

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<?php

if (isset($_POST['product_name']) && isset($_POST['product_description']) && isset($_POST['user_id'])) {
   // Connect

   $link = mysql_connect('mysql_host', 'mysql_user', 'mysql_password');

   if(!is_resource($link)) {

       echo "Failed to connect to the server\n";
       // ... log the error properly

   } else {
       
       // Reverse magic_quotes_gpc/magic_quotes_sybase effects on those vars if ON.

       if(get_magic_quotes_gpc()) {
           $product_name        = stripslashes($_POST['product_name']);
           $product_description = stripslashes($_POST['product_description']);
       } else {
           $product_name        = $_POST['product_name'];
           $product_description = $_POST['product_description'];
       }

       // Make a safe query
       $query = sprintf("INSERT INTO products (`name`, `description`, `user_id`) VALUES ('%s', '%s', %d)",
                   mysql_real_escape_string($product_name, $link),
                   mysql_real_escape_string($product_description, $link),
                   $_POST['user_id']);

       mysql_query($query, $link);

       if (mysql_affected_rows($link) > 0) {
           echo "Product inserted\n";
       }
   }
} else {
   echo "Fill the form properly\n";
}
?>

The query will now execute correctly, and SQL Injection attacks will not work.




Notes
Note:
A MySQL connection is required before using mysql_real_escape_string() otherwise an error of level E_WARNING is generated, and FALSE is returned. If link_identifier isn't defined, the last MySQL connection is used.

Note:
If magic_quotes_gpc is enabled, first apply stripslashes() to the data. Using this function on data which has already been escaped will escape the data twice.

Note:
If this function is not used to escape data, the query is vulnerable to SQL Injection Attacks.

Note:
mysql_real_escape_string() does not escape % and _. These are wildcards in MySQL if combined with LIKE, GRANT, or REVOKE.