Create table with `DEFAULT (now())` fails in AST driver

[wojtekn]

Here is the SQL:

CREATE TABLE `test_now_default` (
  `id` int NOT NULL,
  `updated` timestamp NOT NULL DEFAULT (now()) ON UPDATE CURRENT_TIMESTAMP
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_520_ci;

It should work in MySQL 8.0.