set_post_thumbnail or media_sideload_image adds image multiple times in media library

Question

I am trying to add the featured image to posts and that works, however, the featured image is apparently set everytime I check my post.

<?php 

$post_id = get_queried_object_id();

$bla = "myImageURL";

// Set the image URL
$image_url = $bla;

// Download the image
$image_id = media_sideload_image($image_url, $post_id, '', 'id');

// Check for errors
if (is_wp_error($image_id)) {
    print_r($image_url);
} else {
    // The image was downloaded successfully. Now set it as the featured image for the post
    set_post_thumbnail($post_id, $image_id);
}

?>

So, every time I view my post, it adds the featured image AGAIN to my media library.

How can I prevent that from happening?

I tried:

elseif (!has_post_thumbnail($post_id)) {
    set_post_thumbnail($post_id, $image_id);
}

But sadly this did not work either. The below also did not work (based on answer here below):

<?php 

$post_id = get_queried_object_id();

$bla = MyIMGURL;

// Set the image URL
$image_url = $bla;

'attachment', 'meta_key' => '_wp_attached_file', 'meta_value' => sanitize_file_name(basename($image_url)); if (!$existing_image) { // Image does not exist in the media library, so download it 
$image_id = media_sideload_image($image_url, $post_id, '', 'id'); // Check for errors 
if (is_wp_error($image_id)) { print_r($image_url); } else { // The image was downloaded successfully.


?>

Answer 1

<?php 

$post_id = get_queried_object_id();

$bla = "myImageURL";

// Set the image URL
$image_url = $bla;

// Check if the image already exists in the media library
$existing_image = get_posts(array(
    'post_type' => 'attachment',
    'meta_key' => '_wp_attached_file',
    'meta_value' => sanitize_file_name(basename($image_url))
));

if (!$existing_image) {
    // Image does not exist in the media library, so download it
    $image_id = media_sideload_image($image_url, $post_id, '', 'id');

    // Check for errors
    if (is_wp_error($image_id)) {
        print_r($image_url);
    } else {
        // The image was downloaded successfully. Now set it as the featured image for the post
        set_post_thumbnail($post_id, $image_id);
    }
} else {
    // Image already exists in the media library, so set it as the featured image for the post
    set_post_thumbnail($post_id, $existing_image[0]->ID);
}

?>