<?php
echo get_magic_quotes_gpc();         // 1
echo $_POST['lastname'];             // O\'reilly
echo addslashes($_POST['lastname']); // O\\\'reilly

if (!get_magic_quotes_gpc()) {
    $lastname = addslashes($_POST['lastname']);
} else {
    $lastname = $_POST['lastname'];
}

echo $lastname; // O\'reilly
$sql = "INSERT INTO lastnames (lastname) VALUES ('$lastname')";
?>

http://cn.php.net/get_magic_quotes_gpc

Magic quotes for incoming GET/POST/Cookie data.

This feature has been DEPRECATED as of PHP 5.3.0 and REMOVED as of PHP 6.0.0. Relying on this feature is highly discouraged.

get_magic_quotes_gpc & mysql query

query

PHP