มีวิธี Select ข้อมูลมาเก็บแล้ว นำมาใช้ใหม่โดยไม่ต้อไป select มาใหม่จาก database ไหมครับ

$sql = 'SECT date_register FROM user ORDER BY date_register ASC ';
$query = mysqli_query(sql);
while($result = mysql_fetch_array(query )){
    echo $result['date_register'];
    $sql2 = 'SECT name, surname FROM user WHERE date_register = '.$result['date_register'].' ';
    $query2 = mysqli_query(sql2);
    while($result2 = mysql_fetch_array(query )){
         echo $result2['name'].' '.$result2['surname'];
    }
}

$sql = 'SECT name, surname, date_register FROM user ORDER BY date_register ASC ';
$query = mysqli_query(sql);
$ar_user = array();
while($result = mysql_fetch_assoc(query )){
   array_push($ar_user, $result);
}

foreach ($ar_user as $rs_user) {
   echo $rs_user['date_register'];
   foreach ($ar_user as $rs_user2) {
       if(rs_user['date_register'] == $rs_user2['date_register']){
           echo $rs_user2['name'].' '.$rs_user2['surname'];
       }
   }
}