Mysql- how to select last 100 recodes from a table

Please can anyone help me with this php/mysql code

$view->pch = $db->Query("SELECT from_unixtime(`pauc_date`), `pauc_ad_id`, `pauc_domain`, `pauc_word`, `pauc_referer`, `pauc_ip`, `pauc_country`
                         FROM publisher_ad_units_clicks 
                         WHERE pauc_user_id=?", "i", $USER_ID);

i need to change this query to get only last 100 rows. because table has thousands of rows and slow down the page loading.