Only retrieve posts where post_excerpt has been filled out

Question

The post_excerpt column is a string and is not filterable using “IS NOT NULL” . To query for an empty string you can use the != operator.

function posts_where_excerpt_not_empty( $where ) {
    $where .= " AND post_excerpt != '' ";
    return $where;
}

Also get_posts suppresses filters by default so you will need to call it with suppress filters set to false or use another query method.

$posts = get_posts( array( 'suppress_filters' => FALSE ) );