Why can't I insert data?

$pdo=new PDO("mysql:host=localhost;dbname=t1","root","");
$txt=$_POST["txt"];
$sql="insert into user(txt)values($txt)";
$pdo->exec($sql);

Reply content:

$pdo=new PDO("mysql:host=localhost;dbname=t1","root","");
$txt=$_POST["txt"];
$sql="insert into user(txt)values($txt)";
$pdo->exec($sql);

$sql="insert into user(txt)values('$txt')";

Your txt should be a string type field, remember to add single quotes

Is there any error message? Try another way of writing

// 预处理
$sql = "INSERT INTO `user`(`txt`) VALUES (:txt)";
$stmt = $pdo->prepare($sql);
$stmt->execute([':txt' => $txt]);