php mysql仅在if语句中存在重复项的情况下更新列

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

// 创建连接
$conn = new mysqli($servername, $username, $password, $dbname);

// 检查连接
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}

// 假设我们要检查的列是'email'，并且我们要更新的列是'status'
$email = $_POST['email']; // 假设'email'是从表单提交的
$newStatus = 'active'; // 新的状态值

// 检查是否存在重复项
$sql_check = "SELECT email FROM users WHERE email = ?";
$stmt_check = $conn->prepare($sql_check);
$stmt_check->bind_param("s", $email);
$stmt_check->execute();
$result_check = $stmt_check->get_result();

if ($result_check->num_rows > 0) {
    // 存在重复项，执行更新操作
    $sql_update = "UPDATE users SET status = ? WHERE email = ?";
    $stmt_update = $conn->prepare($sql_update);
    $stmt_update->bind_param("ss", $newStatus, $email);
    if ($stmt_update->execute()) {
        echo "更新成功";
    } else {
        echo "更新失败: " . $stmt_update->error;
    }
} else {
    echo "没有重复项，无需更新";
}

$stmt_check->close();
$stmt_update->close();
$conn->close();
?>

$conn->begin_transaction();
try {
    // 执行检查和更新操作
    $conn->commit();
} catch (Exception $e) {
    $conn->rollback();
    echo "发生错误：" . $e->getMessage();
}