//$sql.= " AND entity IN (0,".$conf->entity.")"; Do not test on entity here. We want to see if there is still on field remaning in other entities before deleting field in table
$resql=$this->db->query($sql);
if($resql)
{
$obj=$this->db->fetch_object($resql);
if($obj->nb<=0)
{
$result=$this->db->DDLDropField(MAIN_DB_PREFIX.$table,$attrname);// This also drop the unique key