如何使用PHP开发微信小程序的日程提醒功能？

CREATE TABLE `reminder` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `openid` varchar(255) NOT NULL,
  `title` varchar(255) NOT NULL,
  `content` text NOT NULL,
  `reminder_time` datetime NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

// 在 app.js 中
App({
  // ...
  globalData: {
    openid: null
  },
  // ...
  onLaunch: function() {
    // 获取用户openid
    wx.login({
      success: function(res) {
        if (res.code) {
          // 调用后端接口获取openid
          wx.request({
            url: 'https://your-backend-domain.com/getOpenid.php',
            data: {
              code: res.code
            },
            success: function(res) {
              // 将openid保存在全局变量中
              getApp().globalData.openid = res.data.openid;
            }
          });
        } else {
          console.log('登录失败！' + res.errMsg);
        }
      }
    });
  },
  // ...
});

wx.request({
  url: 'https://your-backend-domain.com/addReminder.php',
  method: 'POST',
  data: {
    openid: getApp().globalData.openid,
    title: '日程标题',
    content: '日程内容',
    reminder_time: '2022-01-01 10:00:00'
  },
  success: function(res) {
    // 提示用户添加成功
    wx.showToast({
      title: '添加成功',
      icon: 'success',
      duration: 2000
    });
  },
  fail: function(res) {
    console.log('添加失败！' + res.errMsg);
  }
});

// getReminders.php
<?php
header('Content-Type: application/json');

// 连接数据库
$db_host = 'localhost';
$db_user = 'your_username';
$db_password = 'your_password';
$db_name = 'schedule';
$db = new mysqli($db_host, $db_user, $db_password, $db_name);
if ($db->connect_errno) {
  die('连接数据库失败！');
}

// 查询待提醒的日程
$now = date('Y-m-d H:i:s');
$query = "SELECT * FROM reminder WHERE openid = '{$_GET['openid']}' AND reminder_time <= '{$now}'";
$result = $db->query($query);

// 返回查询结果
$reminders = [];
while ($row = $result->fetch_assoc()) {
  array_push($reminders, $row);
}
echo json_encode($reminders);

// 关闭数据库连接
$db->close();
?>

// 在 app.js 中
setInterval(function() {
  wx.request({
    url: 'https://your-backend-domain.com/getReminders.php',
    data: {
      openid: getApp().globalData.openid
    },
    success: function(res) {
      if (res.data.length > 0) {
        // 弹出提醒窗口
        for (var i = 0; i < res.data.length; i++) {
          wx.showModal({
            title: res.data[i].title,
            content: res.data[i].content,
            showCancel: false
          });
        }
      }
    }
  });
}, 60000); // 每分钟轮询一次