如何在mysql和php中修改表列？

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

$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}

$sql = "ALTER TABLE table_name MODIFY column_name new_column_definition";
if ($conn->query($sql) === TRUE) {
    echo "表列修改成功";
} else {
    echo "表列修改失败: " . $conn->error;
}

$conn->close();