可能让PHP MYSQL查询忽略WHERe子句中的空变量？

采用

$where = "WHERe user_id = '$username'";if(!empty($value1)){$where .= "and location = '$value1'";}if(!empty($value2 )){$where .= "and english_name= '$value2 '";}$query = "SELECt * FROM moth_sightings $where";$result = mysql_query($query) or die(mysql_error());$r = mysql_numrows($result);