<?php
if($_POST["action"] == "login")
{
	$query= $db->query("SELECT * FROM mytable WHERE BINARY username ='".$_POST["username"]."' AND password =".$_POST["password"]."'");
	if($db->num_rows($query) > 0)
	{
		echo "succefully loginned";
	}
	else
	{
		echo"wrong username/password";
	}
}
<?
<form method="post">
Username : <input type="text" name="username">
Password : <input type="text" name="password">
<input type="button" value="Login">
</form>