Преобразование выборки к определённому виду

$reply_sep = '|><|';
$field_sep = '<||>';
 
$sql = 'SELECT *, `c_r`.`reply` '
        . 'FROM `complaints` '
        . 'INNER JOIN ('
        . 'SELECT `complaints_reply`.`complaint_id`, '
        . 'GROUP_CONCAT(CONCAT_WS("' . $field_sep . '", `id`,`complaint_id`, `reply_name`, `reply_text`, `reply_date`) SEPARATOR "' . $reply_sep . '") `reply`'
        . 'FROM `complaints_reply` GROUP BY `complaint_id`) `c_r` '
        . 'ON `complaints`.`id` = `c_r`.`complaint_id` '
        . 'WHERE `offer_id` IN (SELECT `id` FROM `offers` WHERE `company_id` = 2)';
 
$result = $mysqli->query($sql);
if ($mysqli->errno)
    die($mysqli->error);
$arr = [];
$reply = ['id', 'complaint_id', 'reply_name', 'reply_text', 'reply_date'];
while ($row = $result->fetch_assoc()) {
    $temp = array_splice($row, 0, 5);
 
    foreach (explode($reply_sep, $row['reply']) as $item) {
        $temp['reply'][] = array_combine($reply, explode($field_sep, $item));
    }
    $arr[] = $temp;
}
 
$json = json_encode(array_values($arr), JSON_UNESCAPED_UNICODE | JSON_PRETTY_PRINT);
echo $json;

'ON `complaints`.`id` = `c_r`.`complaint_id` '

$reply_sep = '|><|';
$field_sep = '<||>';
 
$sql = 'SELECT `id`, `offer_id`, `user_name`, `text`, `date`, `c_r`.`reply` '
     . 'FROM `complaints` '
     . 'LEFT JOIN ('
         . 'SELECT `complaint_id`, GROUP_CONCAT('
             .'CONCAT_WS("' . $field_sep . '", `id`,`complaint_id`, `reply_name`, `reply_text`, `reply_date`) SEPARATOR "' . $reply_sep . '") `reply`'
         . 'FROM `complaints_reply` GROUP BY `complaint_id`) `c_r` '
     . 'ON `complaints`.`id` = `c_r`.`complaint_id` '
     . 'WHERE `offer_id` IN (SELECT `id` FROM `offers` WHERE `company_id` = 2)';
 
$result = $mysqli->query($sql);
if ($mysqli->errno)
    die($mysqli->error);
$arr = [];
$reply = ['id', 'complaint_id', 'reply_name', 'reply_text', 'reply_date'];
while ($row = $result->fetch_assoc()) {
    $temp = array_splice($row, 0, 5);
    $temp['reply'] = [];
    if (!empty($row['reply'])) { 
        foreach (explode($reply_sep, $row['reply']) as $item) {
            $temp['reply'][] = array_combine($reply, explode($field_sep, $item));
        }
    } 
    $arr[] = $temp;
}
 
$json = json_encode(array_values($arr), JSON_UNESCAPED_UNICODE | JSON_PRETTY_PRINT);
echo $json;

$sql = 'SELECT * `c_r`.`reply` '
     . 'FROM `complaints` '
     . 'LEFT JOIN ('
        . 'SELECT `complaint_id`, GROUP_CONCAT('
            . 'CONCAT_WS("' . $field_sep . '", `id`,`complaint_id`, `reply_user_type`, `reply_user_id`, `reply_user_name`, `reply_text`, `reply_date`) SEPARATOR "' . $reply_sep . '") `reply`'
        . 'FROM `complaints_reply` GROUP BY `complaint_id`) `c_r` '
     . 'ON `complaints`.`id` = `c_r`.`complaint_id` '
     . 'WHERE `offer_id` IN (SELECT `id` FROM `offers` WHERE `company_id` = 2)';
 
$result = $mysqli->query($sql);
if ($mysqli->errno)
    die($mysqli->error);
$arr = [];
$reply = ['id', 'complaint_id', 'reply_user_type', 'reply_user_id', 'reply_user_name', 'reply_text', 'reply_date'];
while ($row = $result->fetch_assoc()) {
    $temp = array_splice($row, 0, 6);
    $temp['reply'] = [];
    if (!empty($row['reply'])) {
        foreach (explode($reply_sep, $row['reply']) as $item) {
            $temp['reply'][] = array_combine($reply, explode($field_sep, $item));
        }
    }
    $arr[] = $temp;
}

$arr = [];
 
$sql_offers = 'SELECT `id` FROM `offers` WHERE `company_id` = 2';
$result_offers = $mysqli->query($sql_offers) or die($mysqli->error);
while ($row_offers = $result_offers->fetch_assoc()) {
    $sql_complaints = 'SELECT * FROM `complaints` WHERE `offer_id`=' . $row_offers['id'];
    $result_complaints = $mysqli->query($sql_complaints) or die($mysqli->error);
    while ($row_complaints = $result_complaints->fetch_assoc()) {
        $sql_reply = 'SELECT * FROM `complaints_reply` WHERE `complaint_id`=' . $row_complaints['id'];
        $result_reply = $mysqli->query($sql_reply) or die($mysqli->error);
        $row_complaints['reply'] = [];
        while ($row_reply = $result_reply->fetch_assoc()) {
            $row_complaints['reply'][] = $row_reply;
        }
        $arr[] = $row_complaints;
    }
}
 
$json = json_encode($arr, JSON_UNESCAPED_UNICODE | JSON_PRETTY_PRINT);
 
echo '<pre>', $json;