Write SQL for basic user metrics

You are given a simplified schema for a fictional social app called Nextagram:

• users(user_id PK, username, created_at TIMESTAMP)
• follows(follower_user_id, followed_user_id, created_at TIMESTAMP)
  • each row means follower_user_id follows followed_user_id

Assume created_at is a timestamp (timezone handling is ignored for this part).

Write SQL queries to answer:

1. How many users are there?

2. In which month did the most users join? (Return the month and the count.)

3. What is the username of the user with the most followers? (If there is a tie, return all tied users.)