$pdo->exec($sql);為什麼總是回傳false

Question

$pdo = new PDO($dsn,$username,$password);

var_dump($pdo);//輸出為object(PDO)#1 (0) { } 

#//執行插入語句 

$sql = "update text set age=age 1 where id=5";

$records = $pdo ->exec($sql);

var_dump($records);