Get 30 days prior data for each row of query - sql

Question

I have a query where I have a list of ~ 20k users for a specific week of the month that represents that they have logged on to our site.
What I need to get - for each of these users, in the past 30 days if they have
1. logged on: defined by any rows recorded in the same table
2. max event in the 30 day window, prior to the date in the current where clause
This is the current code snippet that helps me narrow to the ~20k users for a given week to begin with:
select
user_id,
max(timestamp)
from table
where timestamp between '2019-02-01' and '2019-02-05'
group by 1,2;
Expected result set/columns:
user_id,
max(timestamp),
logged_on, [if they have any # of rows in the same table within 30 days prior to their max(timestamp) date]
previous_timestamp, [the 2nd most recent login date within 30 days prior to their max(timestamp) date]

Answer 1

I think this is what you're looking for. Not sure if it's the most efficient method though - perhaps windowing functions may perform better but like bob-mccormick mentioned: the tricky bit would be filling in dates where the user (partition key) was not active so that the range query will work correctly.
Example data setup (Snowflake syntax)
-- Create sample table
create temporary table user_logins (userid number, date_logged_on timestamp);
;
-- Insert some random sample data
insert overwrite into user_logins
select
uniform(1,10,random()) userid,
dateadd('minutes', uniform(1,86400,random()) * -1,current_timestamp::timestamp_ntz) date_logged_on
from table(generator(rowcount => 100))
;
Select statement
-- Run select
with user_last_logins as (
select
userid,
max(date_logged_on) last_login
from user_logins
where
date_logged_on between '2019-01-01' and '2019-05-08'
group by userid
)
select
user_last_logins.userid,
max(user_last_logins.last_login) last_logged_on,
count(prior_30_each_user.userid) num_logins_prior_30,
max(prior_30_each_user.date_logged_on)
from user_last_logins
left join user_logins prior_30_each_user
on user_last_logins.userid = prior_30_each_user.userid
and prior_30_each_user.date_logged_on > dateadd('day', -30, user_last_logins.last_login) and prior_30_each_user.date_logged_on < user_last_logins.last_login
group by user_last_logins.userid
;