how can i allow users to view their own pending posts in a front-end page

According to WordPress Codex is a post status that awaits a user with the publish_posts capability (typically a user assigned the Editor role) to publish. (pending)

In other words, a post that is pending is a post that is not published meaning that it can not be viewed by not registered users with at least the publish_posts capability (Editor etc). So public users can not view the post. That’s why the url is not “working”.

The database just keeps the post status of the post. WordPress Core is responsible for handling the posts depending their status. Also I would suggest to not alter by no means the database manually and always use the WordPress API to modify WordPress elements like posts, pages etc