Syntax error SQLSTATE[42000]

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SQL

PHP

I have a problem with syntax i don't have any idea how i fix it. Please help me.

Error: SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'where idpost= '2'' at line 1

$PDO->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$zmienna = "INSERT INTO `comments` (`iduser`, `comment`, `nick_user`) VALUES (:iduser, :comment, :nick_user) where idpost= :idpost ";
$stmt = $PDO->prepare($zmienna);
$stmt->bindValue(':idpost', $article['id'], PDO::PARAM_INT );

What I have tried:

PDO::PARAM_INT
$zmienna = "INSERT INTO `comments` (`iduser`, `comment`, `nick_user`) VALUES (:iduser, :comment, :nick_user) where idpost= ".$article['id']." ";