$sql = 'SELECT COUNT( DATE_R ) , Heures1, Heures1bis, DATE_FORMAT(DATE_R,'%d/%m/%Y') ,DATE_R'
. ' FROM retenues '.$clause
. ' GROUP BY DATE_R, Heures1 '
. ' ORDER BY DATE_R DESC , Heures1 DESC';UPDATE ta_table
SET nouvelle_date = STR_TO_DATE(ancienne_date, '%d/%m/%Y')