select id,
( cast(current_timestamp as date) - cast(return_date as date) ) * 3 as fine
from books
where
return_date > current_timestamp


This is how to do the select in postgresql however...

select *
from table
where date >= [start date] and date <= [end date]

or (i'm not 100% sure if this works in mysql but it does in postgres!)

select *
from table
where date between [start...

No problem. I when you said 'i have two servers' I assumed you were talking about work.

If you're starting I recommend this (http://php.about.com/od/learnphp/p/learn_php_free.htm). Also, the php...

$connection = mysql_connect(IP_ADDRESS_OF_DATABASE_SERVER:PORT_YOU_SET_MYSQL_TO_LISTEN_ON, DB_USER, DB_PASS)
or die("Query failed : " . mysql_error());
$db = mysql_select_db(DB_NAME,...

Just set the host parameter of the mysql_connect function to the IP address of the other server. You'll also need to open the MySQL port (3306) on the other server if it's closed