$username = "jim";
$password = "bob";

$sql="SELECT * FROM users WHERE login = '".$username."' AND password = '".$password."'";

// Execute the SQL statement
// results stored in the $rs variable.

$rs = mysql_query($sql);

// determine of the mysql_query() was successful

if(!$rs) {
$err=mysql_error();
print $err;
exit();
}

// If was successful, check returned result
// mysql_affected_rows() will return the number of rows affected

if(mysql_affected_rows()==0){
print "Username/password pair is invalid. Please try again.";
} else {
// display last logged in time
$row=mysql_fetch_array($r);
$last=$row["last_logged_in"];
print "Login successful. (You last logged in at ".$last.".)";
}