lateral_join_funnel_2.sql

SELECT 
  sum(view_homepage) AS viewed_homepage,
  sum(use_demo) AS use_demo,
  sum(enter_credit_card) AS entered_credit_card
FROM (
  -- Get the first time each user viewed the homepage.
  SELECT
    user_id,
    1 AS view_homepage,
    min(time) AS view_homepage_time
  FROM event
  WHERE
    data->>'type' = 'view_homepage'
  GROUP BY user_id
) e1 LEFT JOIN LATERAL (
  -- For each row, get the first time the user_id did the use_demo
  -- event, if one exists within one week of view_homepage_time.
  SELECT
    user_id,
    1 AS use_demo,
    time AS use_demo_time
  FROM event
  WHERE
    user_id = e1.user_id AND
    data->>'type' = 'use_demo' AND
    time BETWEEN view_homepage_time AND (view_homepage_time + 1000*60*60*24*7)
  ORDER BY time
  LIMIT 1
) e2 ON true LEFT JOIN LATERAL (
  -- For each row, get the first time the user_id did the enter_credit_card
  -- event, if one exists within one week of use_demo_time.
  SELECT
    1 AS enter_credit_card,
    time AS enter_credit_card_time
  FROM event
  WHERE
    user_id = e2.user_id AND
    data->>'type' = 'enter_credit_card' AND
    time BETWEEN use_demo_time AND (use_demo_time + 1000*60*60*24*7)
  ORDER BY time
  LIMIT 1
) e3 ON true