You need to escape your POST values before you insert put them into your query. You should escape your POST values before you use them in a database query.
Instead of this:
$data = mysql_query("SELECT * from users where user_name == ($_POST['user_name']) and ($_POST['password']) and ($_POST['user_type'])"
Do this:
$user_name = mysql_real_escape_string($_POST['user_name']);
$password = mysql_real_escape_string($_POST['password']);
$user_type = mysql_real_escape_string($_POST['user_type']);
$data = mysql_query("SELECT * FROM users WHERE user_name == '$user_name' AND password == '$password' AND user_type == '$user_type'");
Note that I am assuming your columns in the table are 'user_name', 'password', and 'user_type'.
