我想手动将时间戳值插入mysql数据库：

$timestamp = "2018-05-15 00:00:00";
  $name = "Fred";

  $pdo = $db->prepare('INSERT INTO data (timestamp,name) values(:timestamp,:name)');
  $pdo->execute(array(
       ':timestamp' => $timestamp,
       ':name' => $name
  ));

但它总是插入现在的日期，而不是变量的日期。
mysql表：

id | timestamp | name
----------------------
   |           |

id = int(11) AUTO_INCREMENT
timestamp = timestamp (Standard: CURRENT TIMESTAMP, Attribute: ON UPDATE CURRENT TIMESTAMP)
name = varchar (255)