add custom field to all post based on post thumbnail

update-thumbnail.php

<?php 
include '../../../wp-load.php';

    $args = array(
        'posts_per_page'   	=> -1,
        'post_type'        	=> 'post',
		'post_status' 		=> 'publish',
        'suppress_filters' 	=> true,
    );
    $posts_array = get_posts( $args );
	
	foreach($posts_array as $post_array) {
		
		if ( has_post_thumbnail($post_array) ) :
		
			$image_key_exists = metadata_exists( 'post', $post_array->ID, 'mwp_thumbnail_url' );
			$image = wp_get_attachment_image_src( get_post_thumbnail_id($post_array->ID), 'full' );
			$url = $image['0'];
		
			if($image_key_exists == true && !empty($image_key_exists) ) {
				update_post_meta($post_array->ID, 'mwp_thumbnail_url', $url, true );
			} else {
				add_post_meta($post_array->ID, 'mwp_thumbnail_url', $url, true );
			}
		endif;
		
    }

?>