以下是一个简单的PHP计件系统实例，用于展示如何使用PHP和MySQL数据库来跟踪和计算用户的计件。
系统需求
- PHP环境
- MySQL数据库
- HTML/CSS进行前端展示
数据库结构
```sql
CREATE TABLE `tasks` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`task_name` varchar(255) NOT NULL,
`status` tinyint(1) NOT NULL DEFAULT '0',
PRIMARY KEY (`id`)
);
CREATE TABLE `task_records` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`task_id` int(11) NOT NULL,
`user_id` int(11) NOT NULL,
`time_spent` int(11) NOT NULL,
`date` datetime NOT NULL,
PRIMARY KEY (`id`),
KEY `task_id` (`task_id`),
KEY `user_id` (`user_id`),
CONSTRAINT `task_records_ibfk_1` FOREIGN KEY (`task_id`) REFERENCES `tasks` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `task_records_ibfk_2` FOREIGN KEY (`user_id`) REFERENCES `users` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
);
```
PHP源码
```php
// 连接数据库
$host = 'localhost';
$dbname = 'your_database';
$username = 'your_username';
$password = 'your_password';
try {
$pdo = new PDO("
