subquery.sql

# Flags users with a pageview during 2019. Faster than joining!
select 
  user.id,
  exists(
    select 1 
    from pageviews 
    where pageviews.user_id=users.id 
      and pageviews.created_at between '2019-01-01' and '2020-01-01'
    limit 1
  ) as "active_2019" 
from users