Supprimer les statistiques à partir de la date choisie :

DELETE g FROM `ps_guest` g INNER JOIN `ps_connections`c USING(id_guest) WHERE c.`date_add`<'2015-01-01';
DELETE FROM `ps_connections` WHERE `date_add`<'2015-01-01';
DELETE FROM `ps_connections_source` WHERE `date_add`<'2015-01-01';
DELETE FROM `ps_connections_pagenotfound` WHERE `date_add`<'2015-01-01';

OPTIMIZE TABLE `ps_guest`;
OPTIMIZE TABLE `ps_connections`;
OPTIMIZE TABLE `ps_connections_source`;
OPTIMIZE TABLE `ps_pagenotfound`;