marked user with label by time for each month - sql

Question

Data source
User ID
Visit Date
1
2020-01-01 12:29:15
1
2020-01-02 12:30:11
1
2020-04-01 12:31:01
2
2020-05-01 12:31:14
Problem
I need advice im trying to do sub query for this result to mark user as retention if they havent visit back for 3 month. i using this query for the data to get user's latest visit each month includes null
select u.user_id, gs.yyyymm, s.last_visit_date
from (select distinct user_id from source s) u cross join
generate_series('2021-01-01'::timestamp, '2021-12-01'::timestamp, interval '1 month'
) gs(yyyymm) left join lateral
(select max(s.visit_date) as last_visit_date
from source s
where s.user_id = u.user_id and
s.visit_date >= gs.yyyymm and
s.visit_date < gs.yyyymm + interval '1 month'
) s
on 1=1;
but i think its really affect to performance if user keep increasing, do you guys have any advice to achieve result like below?
Expected Result
Month
User ID
Type
1
1
FIRST
2
1
RETENTION
3
1
RETENTION
4
1
REACTIVATE
....
12
1
null
1
2
null
...
5
2
FIRST
6
2
RETENTION
7
2
RETENTION
8
2
RETENTION
9
2
null
... and so on
or it could be like this
Month
First
Retention
Reactiavate
1
1
0
0
2
0
1
0
3
0
1
0
4
0
0
1
5
1
0
0
6
0
1
0
7
0
1
0
8
0
1
0
9
0
0
0
... and so on

Answer 1

My solution have some reasonable requirements, but I can work without it (the price is some performance).
I built some helper tables what is autofilled with trigger.
The requirement is, that UPDATE or DELETE isn't allowed on visit table.
mst_user table stores distinct user_id-s and it's first_visit.
user_monthly_visit table stores the last and the first visit_date pro user_id and month.
TABLES
CREATE TABLE mst_user (
id BIGINT,
first_visit TIMESTAMP,
CONSTRAINT pk_mst_user PRIMARY KEY (id)
);
CREATE TABLE visit (
user_id BIGINT,
visit_date TIMESTAMP,
CONSTRAINT visit_user_fkey FOREIGN KEY (user_id) REFERENCES mst_user (id)
);
CREATE TABLE user_monthly_visit (
user_id BIGINT,
month DATE,
first_visit_this_month TIMESTAMP,
last_visit_this_month TIMESTAMP,
CONSTRAINT pk_user_monthly_visit PRIMARY KEY (user_id, month),
CONSTRAINT user_monthly_visit_user_fkey FOREIGN KEY (user_id) REFERENCES mst_user (id)
);
CREATE INDEX ix_user_monthly_visit_month ON user_monthly_visit(month);
TRIGGER
CREATE OR REPLACE FUNCTION trf_visit() RETURNS trigger
VOLATILE
AS $xx$
DECLARE
l_user_id BIGINT;
l_row RECORD;
l_user_monthly_visit user_monthly_visit;
BEGIN
IF (tg_op = 'INSERT')
THEN
l_row := NEW;
INSERT INTO mst_user(id, first_visit) VALUES (l_row.user_id, l_row.visit_date)
ON CONFLICT(id) DO UPDATE SET first_visit = LEAST(mst_user.first_visit, l_row.visit_date);
INSERT INTO user_monthly_visit(user_id,month,first_visit_this_month,last_visit_this_month) VALUES (l_row.user_id,date_trunc('month',l_row.visit_date),l_row.visit_date,l_row.visit_date)
ON CONFLICT(user_id,month) DO UPDATE SET first_visit_this_month = LEAST(user_monthly_visit.first_visit_this_month,l_row.visit_date),
last_visit_this_month = GREATEST(user_monthly_visit.last_visit_this_month,l_row.visit_date);
ELSE
RAISE EXCEPTION 'UPDATE and DELETE arent allowed!';
END IF;
RETURN l_row;
END;
$xx$ LANGUAGE plpgsql;
CREATE TRIGGER trig_visit
BEFORE INSERT OR DELETE OR UPDATE ON visit
FOR EACH ROW
EXECUTE PROCEDURE trf_visit();
TESTDATA
INSERT INTO visit (user_id, visit_date)
VALUES (1, '20200101 122915');
INSERT INTO visit (user_id, visit_date)
VALUES (1, '20200102 123011');
INSERT INTO visit (user_id, visit_date)
VALUES (1, '20200401 123101');
INSERT INTO visit (user_id, visit_date)
VALUES (2, '20200501 123114');
QUERY
SELECT mnt AS month, user_id,
CASE WHEN first_visit IS NULL OR first_visit> yyyymm + INTERVAL '1 month' THEN NULL
WHEN first_visit_this_month = first_visit THEN 'FIRST'
WHEN first_visit_this_month IS NULL AND last_three_month + INTERVAL '3 month' >= yyyymm THEN 'RETENTION'
WHEN first_visit_this_month IS NOT NULL THEN 'REACTIVATE'
ELSE NULL
END user_type
FROM
(SELECT date_part('month', gs.yyyymm)::INTEGER AS mnt, gs.yyyymm, u.id user_id, umv.first_visit_this_month, umv.last_visit_this_month, u.first_visit,
GREATEST(
LAG(last_visit_this_month) OVER w,
LAG(last_visit_this_month,2) OVER w,
LAG(last_visit_this_month,3) OVER w
) last_three_month
FROM
generate_series('2020-01-01'::TIMESTAMP, '2020-12-01'::TIMESTAMP, INTERVAL '1 month') gs(yyyymm)
CROSS JOIN mst_user u
LEFT JOIN user_monthly_visit umv on (umv.user_id=u.id AND umv.month = gs.yyyymm)
WINDOW w AS (PARTITION BY u.id ORDER BY gs.yyyymm)
) monthly_visit
ORDER BY user_id,mnt;
RESULT
month
user_id
user_type
1
1
FIRST
2
1
RETENTION
3
1
RETENTION
4
1
REACTIVATE
5
1
RETENTION
6
1
RETENTION
7
1
RETENTION
8
1
(null)
9
1
(null)
10
1
(null)
11
1
(null)
12
1
(null)
1
2
(null)
2
2
(null)
3
2
(null)
4
2
(null)
5
2
FIRST
6
2
RETENTION
7
2
RETENTION
8
2
RETENTION
9
2
(null)
10
2
(null)
11
2
(null)
12
2
(null)

Answer 2

restating your question so it is clearer for me:
for any given month, the user is classified as first, retention or reactivate based on the following criteria
first: month of first visit
retention: within 3 months since previous visit
reactivate: month of visit & no visit in prior month
If I understood this correctly, you can get the first desired result with the following query
Schema (PostgreSQL v13)
create table visits (user_id int, visit_at timestamp);
insert into visits values
(1, '2020-01-01 12:29:15'),
(1, '2020-01-02 12:30:11'),
(1, '2020-04-01 12:31:01'),
(2, '2020-05-01 12:31:14');
Query
WITH trange AS (
SELECT
user_id
, DATE_TRUNC('month', min(visit_at)) visit_from
, DATE_TRUNC('month', max(visit_at)) + interval '3 month' visit_to
FROM visits
GROUP BY 1
)
, monthly_visits AS (
SELECT DISTINCT
user_id
, DATE_TRUNC('month', visit_at) visit_month
FROM visits
)
SELECT
trange.user_id
, DATE(m) report_month
, CASE
WHEN visit_from = m THEN 'FIRST'
WHEN visit_month = m AND LAST_VALUE(visit_month) OVER w IS NULL THEN 'REACTIVATE'
WHEN m <= MAX(visit_month) OVER w + INTERVAL '3 MONTH' THEN 'RETENTION'
ELSE NULL END user_type
FROM trange
LEFT JOIN LATERAL GENERATE_SERIES(visit_from, visit_to, '1 month') m(m)
ON true
LEFT JOIN monthly_visits
ON monthly_visits.user_id = trange.user_id
AND monthly_visits.visit_month = m.m
WINDOW w AS (
PARTITION BY trange.user_id
ORDER BY m.m
ROWS BETWEEN UNBOUNDED PRECEDING AND 1 PRECEDING
);
user_id
report_month
user_type
1
2020-01-01T00:00:00.000Z
FIRST
1
2020-02-01T00:00:00.000Z
RETENTION
1
2020-03-01T00:00:00.000Z
RETENTION
1
2020-04-01T00:00:00.000Z
REACTIVATE
1
2020-05-01T00:00:00.000Z
RETENTION
1
2020-06-01T00:00:00.000Z
RETENTION
1
2020-07-01T00:00:00.000Z
RETENTION
2
2020-05-01T00:00:00.000Z
FIRST
2
2020-06-01T00:00:00.000Z
RETENTION
2
2020-07-01T00:00:00.000Z
RETENTION
2
2020-08-01T00:00:00.000Z
RETENTION
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