Insert post metadata for all posts in CPT at once if metadata no existent

To anyone interested this is the query that worked for me:

INSERT INTO $wpdb->postmeta (post_id,meta_key,meta_value)
SELECT p.ID, 'score' AS meta_key, 0 AS meta_value
FROM $wpdb->posts AS p
WHERE p.post_type="my_cpt"
AND p.ID NOT IN (
    SELECT p2.ID 
    FROM $wpdb->posts AS p2
    INNER JOIN $wpdb->postmeta AS pm
    ON pm.post_id = p2.ID
    WHERE pm.meta_key = 'score'
)

But after reading this article I preferred to split the query in two for better performance:

global $wpdb;

//Get all posts which already have the metadata
$not_in = $wpdb->get_results( 
    "
    SELECT p.ID
    FROM $wpdb->posts AS p
    INNER JOIN $wpdb->postmeta AS pm
    ON pm.post_id = p.ID
    WHERE pm.meta_key = 'score'
    AND p.post_type="my-cpt"
    AND p.post_status NOT IN ('draft,auto-draft')",
    ARRAY_A
);

//Make results into string
$not_in = ! empty($not_in) ? implode( ',', array_column( $not_in, 'ID' ) ) : '';

//Insert new metadata
$wpdb->query(
    "
    INSERT INTO $wpdb->postmeta (post_id,meta_key,meta_value)
    SELECT p.ID, 'score' AS meta_key, 0 AS meta_value
    FROM $wpdb->posts AS p
    WHERE p.post_type="my-cpt"
    AND p.ID NOT IN ( $not_in )
    "
);