如何过滤while循环中的项目？ [复制]答案

【问题标题】：How to filter items in while loop? [duplicate]如何过滤while循环中的项目？ [复制]
【发布时间】：2021-12-22 17:08:28
【问题描述】：

SQL 表 [订单]

| orderId | dueDate    | emailAddress   |
| ------- | ---------- | -------------- |
| 1010101 | 10/11/2021 | joe@gmail.com  |
| 1010102 | 10/11/2021 | joe@gmail.com  |
| 1010103 | 10/11/2021 | joe@gmail.com  |
| 1010104 | 10/11/2021 | john@gmail.com |
| 1010105 | 10/11/2021 | john@gmail.com |
| 1010106 | 10/11/2021 | john@gmail.com |

PHP 脚本

$query = "SELECT * FROM orders";
$result = mysqli_query($conn, $query);
while ($row = mysqli_fetch_assoc($result)) {
  $order = $row['orderId'];
  $to = $row['emailAddress'];
  $sub = "Payment Due Reminder";
  $body = "Due reminder message with order ID $order";
  mail($to, $sub, $body);
}

我的要求

现在我只想发送一封列出三个订单 ID 的电子邮件，而不是向同一个收件人发送三封电子邮件。有没有办法实现？

【问题讨论】：

标签： php mysql while-loop

【解决方案1】：

我会在 MySQL 中使用聚合查询来处理这个问题：

$query = "SELECT dueDate, emailAddress, GROUP_CONCAT(orderId) AS all_orders
FROM orders
GROUP BY dueDate, emailAddress";

$result = mysqli_query($conn, $query);
while ($row = mysqli_fetch_assoc($result)) {
    $all_orders = $row['all_orders'];
    $to = $row['emailAddress'];
    $sub = "Payment Due Reminder";
    $body = "Due reminder message with order ID $all_orders";
    mail($to, $sub, $body);
}

【讨论】：