I\'m using this php to fetch data from my mysql database:
$wpdb->get_var(\"select count(*) from \" . $wpdb->prefix . \"newsletter where status=\'C\'\")
There is affffdate() function in MySQL wich you can use for this :)
$wpdb->get_var("select count(*) from " . $wpdb->prefix . "newsletter where status='C' and date_format(created,'%Y%m%d')>date_format(affffdate(now(),interval -30 day),'%Y%m%d')");
This one is for 30 days back but you can replace the "interval -30 day" with "interval -1 month" or visit dev.mysql where you have all explained.
Hope it helps.