如何在PHP和MySQL中生成循环赛？

在PHP和MySQL中生成循环赛，可以通过以下步骤实现：

创建一个数据库表，用于存储参赛者和他们的分组信息。

CREATE TABLE participants (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(255) NOT NULL,
    group_id INT NOT NULL
);

创建一个数据库表，用于存储循环赛的轮次和匹配信息。

CREATE TABLE rounds (
    id INT AUTO_INCREMENT PRIMARY KEY,
    round_number INT NOT NULL,
    participant1_id INT NOT NULL,
    participant2_id INT NOT NULL,
    winner_id INT,
    FOREIGN KEY (participant1_id) REFERENCES participants(id),
    FOREIGN KEY (participant2_id) REFERENCES participants(id),
    FOREIGN KEY (winner_id) REFERENCES participants(id)
);

编写PHP代码，生成循环赛的轮次和匹配信息。

<?php
// 获取所有参赛者
$participants = $db->query("SELECT * FROM participants ORDER BY group_id")->fetchAll(PDO::FETCH_ASSOC);

// 获取参赛者数量
$num_participants = count($participants);

// 生成循环赛匹配
for ($i = 0; $i < $num_participants; $i++) {
    $round_number = ($i + 1) / 2;
    $participant1_id = $participants[$i]['id'];
    $participant2_id = $participants[($i + $num_participants / 2) % $num_participants]['id'];

    // 插入循环赛匹配信息
    $db->query("INSERT INTO rounds (round_number, participant1_id, participant2_id) VALUES ($round_number, $participant1_id, $participant2_id)");
}

编写PHP代码，查询循环赛的轮次和匹配信息。

<?php
// 查询循环赛匹配信息
$rounds = $db->query("SELECT * FROM rounds ORDER BY round_number")->fetchAll(PDO::FETCH_ASSOC);

// 输出循环赛匹配信息
foreach ($rounds as $round) {
    $participant1 = $db->query("SELECT name FROM participants WHERE id = {$round['participant1_id']}")->fetchColumn();
    $participant2 = $db->query("SELECT name FROM participants WHERE id = {$round['participant2_id']}")->fetchColumn();
    $winner = $round['winner_id'] ? $db->query("SELECT name FROM participants WHERE id = {$round['winner_id']}")->fetchColumn() : '';

    echo "Round {$round['round_number']}: {$participant1} vs {$participant2} - Winner: {$winner}\n";
}

通过以上步骤，可以在PHP和MySQL中生成循环赛。