PHP MYSQL防止基于某些列的重复

CREATE TABLE users (
    id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(50),
    email VARCHAR(50) UNIQUE,
    password VARCHAR(50)
);

$email = $_POST['email'];

// 查询数据库
$query = "SELECT COUNT(*) as count FROM users WHERE email = '$email'";
$result = mysqli_query($connection, $query);
$row = mysqli_fetch_assoc($result);

if ($row['count'] > 0) {
    // 存在重复值，处理逻辑
} else {
    // 插入或更新数据
}

$email = $_POST['email'];

// 开始事务
mysqli_begin_transaction($connection);

// 查询数据库
$query = "SELECT COUNT(*) as count FROM users WHERE email = '$email'";
$result = mysqli_query($connection, $query);
$row = mysqli_fetch_assoc($result);

if ($row['count'] > 0) {
    // 存在重复值，回滚事务
    mysqli_rollback($connection);
} else {
    // 插入或更新数据
    // ...

    // 提交事务
    mysqli_commit($connection);
}