Hi navixeldeveloper,
It might help to see the code. Can you post the code that you’re working with into a pastebin, or a Github gist or similar and post the link here?
If you are using the WP_Query class to get the posts, you could add an 'orderby' => 'meta_value', argument to the arguments array when you instantiate the class. But then you must also provide a ‘meta_key’ argument, which will exclude posts with no meta value.
You could get the keyless posts as a separate query and list them either before or after the other posts, which is where they would be anyway if they could have been part of the meta_key query.
The only other alternative would be to write your own SQL query and execute it using $wpdb methods.