如何使用 PHP 函数与数据库交互？

$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "database";

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

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

$sql = "SELECT * FROM users";
$result = $conn->query($sql);

// 检查查询是否成功
if (!$result) {
    die("查询失败: " . $conn->error);
}

while ($row = $result->fetch_assoc()) {
    echo $row["name"] . "<br>";
}

$sql = "INSERT INTO users (name) VALUES ('John Doe')";

if ($conn->query($sql) === TRUE) {
    echo "记录已成功插入";
} else {
    echo "插入记录失败: " . $conn->error;
}

$sql = "UPDATE users SET name='John Smith' WHERE id=1";

if ($conn->query($sql) === TRUE) {
    echo "记录已成功更新";
} else {
    echo "更新记录失败: " . $conn->error;
}

$sql = "DELETE FROM users WHERE id=1";

if ($conn->query($sql) === TRUE) {
    echo "记录已成功删除";
} else {
    echo "删除记录失败: " . $conn->error;
}

$conn->close();