URL rewriting and redirection - apache

Question

I just finished my rewriting with .htaccess and everything works just fine.
RewriteEngine on
RewriteRule blog/([a-zA-Z0-9\-]+)-([0-9]+) post.php?url=1&id=$2
The only I want to avoid is the duplicate content... I've searched a lot on the subject and sadly found anything matches my needs.
The fact is, the rewrited address "blog/my-new-post-77" is also accessible by "post.php?id=77" and I don't want it to happen. So I would like to redirect every post.php pages to the rewrited rule.
Someone have an idea for me?

Answer 1

Yes, add extra variable to your rewrite rule to check it:
RewriteRule blog/([a-zA-Z0-9\-]+)-([0-9]+) post.php?check=ok&url=$1&id=$2
And at the top of your post.php file, check for that check variable:
if(isset($_GET['check'])){
if($_GET['check'] == "ok"){
//it comes using rewrite rule
//cut and paste all of your codes in post.php file to here
//that is which codes are available when user view your page in desired way
//don't redirect to rewrite rule again here, since visitor came using that rewrite rule to here. doing so will result infinite redirect and will show an error
}else{
//this visit is not used rewrite rule to come here
//here you can redirect visitor to not found page or just show an empty page by putting die();
//you can't redirect to post pages here, because you don't know what post(id) that visitor need to see
}
}else{
//this visit is not used rewrite rule to come here
//here you can redirect visitor to not found page or just show an empty page by putting die();
//you can't redirect to post pages here, because you don't know what post(id) that visitor need to see
}

Answer 2

post.php?id=77 -> /my-new-post-77 via the browser
/my-new-post-77 -> post.php?id=77 via internal rewrite
Is it right?
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule blog/([a-zA-Z0-9\-]+)\-([0-9]+)$ post.php?url=1&id=$2 [L]
RewriteCond %{THE_REQUEST} \s\/post\.php\?id\=(\d+)\s
RewriteRule . /my-new-post-%1 [R,L]

Answer 3

I found a solution which matches my needs waaaay more.
if($data["url"]!=$_GET["url"]) {
header("Location:http://www.mywebsite.com/blog/".$data["url"]."-".$data["id"]);
}
This solution forces the post.php?id=XX to go to the rewrited location as we wanted and by the same time, encounter any manual url rewriting.
$result being the SELECT ALL of my databases rows.
$data = mysqli_fetch_array($result);
I tested #Janaka solution, with your great explanations, and it worked tho.
Thanks everybody; Case closed :)