<?php
        $user = $username;

        $timestamp = time();
        $date = date("Y.m.d", $timestamp);

        // Look if the user has writed something..
        $sql="SELECT user, date FROM book WHERE user='$user' AND date=???";
        $qry=mysql_query($sql);
        $num_rows = mysql_num_rows($qry);
        mysql_query($sql);

        if($num_rows > 0) {
        ?>

        Today you have writed.

        <?php
        } else {
        ?>

        Action....

        <?php } ?>