Relational Algebra Queries for User, Post, and Comment Database

Find the uid of the youngest user(s). π uid (σ age = min(age)(User))

Find the number of posts made by each user uid. γ uid, count(pid) (Post)

Find the username of user who does not make any post or comment. π username (User - (π username (User ⨝ Post ⨝ Comment)))

Find the uid of user who comments all the posts made by username 'Alan Turing'. π uid ((π uid (User ⨝ username = 'Alan Turing'(User))) ⨝ Comment)