I am working on a forum system and I need to delete all topics and posts from a particular forum.

There is a `posts` table that holds all the posts. Each post has `topic_id` field which is the ID of the topic to which it belongs. The topics reside in `topics` table and each topic has `forum_id` field which is the ID of the forum it belongs to.

So now when I decide to delete forum with ID `1`, how would I go about deleting all topics and posts from this forum as well?