Mysql - 带select和PDO的条件插入查询

I am unable to understand on how to apply insert query with select statement:

I have gone through this question also:

MySQL INSERT from a SELECT with PDO

But where is the VALUES part??

Like I have this query to insert in Mysql and here I use Values also:

$db_conn->beginTransaction();
$query = $db_conn->prepare('INSERT INTO mytable (name, user_id) VALUES(:sname, :uid)');
foreach($UploadData AS $DataValue)
{
    $query->execute(array(':sname' => $DataValue['Name'],':uid' =>$_SESSION['uid']));
}
$db_conn->commit();

My motto is to check if the name exists with the same uid it shouldn't import the data otherwise it should. But Where are the values part :/ I am blind :P

EDIT1: From MySQL INSERT from a SELECT with PDO

How will this code block work if no VALUES is supplied?

$sql_enc = '
    INSERT INTO sessionid (enc_id, enc_pass, enc_date) 
        (SELECT AES_ENCRYPT(username, :aeskey), AES_ENCRYPT(pwd, :aeskey), DATE_ADD(NOW(), INTERVAL 15 SECOND) FROM users WHERE username = :username)
';
$res_enc = $pdo->prepare($sql_enc);
$res_enc->bindParam(':aeskey', $aeskey);
$res_enc->bindParam(':username', $username);
$res_enc->bindParam(':pwd', $username);
$res_enc->execute();
$res_enc = null;