Get rolling 30 day count of users logging in to site - sql

Question

I have a table of login to my site in the format below:
logins
+---------+--------------------------+-----------------------+
| USER_ID | LOGIN_TIMESTAMP | LOGOUT_TIMESTAMP |
+---------+--------------------------+-----------------------+
| 274385 | 01-JAN-20 02.56.12 PM | 02-JAN-20 10.04.40 AM |
| 32498 | 01-JAN-20 05.12.14 PM | 01-JAN-20 08.26.43 PM |
| 981231 | 01-JAN-20 04.41.04 PM | 01-JAN-20 10.51.11 PM |
+---------+--------------------------+-----------------------+
I would like to calculate a unique count of users who logged in only once in the previous 30 days, per day to get something as below
(note - USER_COUNT_LAST_30_DAYS counts only those users who logged in only once in the previous 30 days)
:
+-----------+-------------------------+
| DAY | USER_COUNT_LAST_30_DAYS |
+-----------+-------------------------+
| 01-JAN-20 | 14 |
| 02-JAN-20 | 23 |
| 03-JAN-20 | 29 |
+-----------+-------------------------+
My first thought would be a query as below, but I recognise this would just count all users who logged in the last 30 days, rather than those who only logged in once
SELECT
CAST(LOGIN_TIMESTAMP AS DATE),
COUNT(DISTINCT USER_ID)
FROM
logins
WHERE
LOGIN_TIMESTAMP > SYSDATE - 30
GROUP BY
CAST(LOGIN_TIMESTAMP AS DATE);
Would this query work in getting me a count of users who logged in only once the last 30 days with a rownum partition filter on user id? or is there something that I would have to ensure to get a rolling 30 day count?

Answer 1

The date datatype still has a time component, even if the format mask doesn't show it. You can use the TRUNC function on either a date or a timestamp. If you really want your day to be limited to the day, you'll need to truncate the timestamp. You also need to use INTERVAL, as timestamp math and date math are not the same:
SELECT TRUNC(LOGIN_TIMESTAMP) LOGIN_DATE,
COUNT(DISTINCT USER_ID) USER_COUNT
FROM logins
WHERE TRUNC(LOGIN_TIMESTAMP) > TRUNC(SYSTIMESTAMP - INTERVAL '30' DAY)
GROUP BY TRUNC(LOGIN_TIMESTAMP)
ORDER BY TRUNC(LOGIN_TIMESTAMP) ASC;
Example:
alter session set nls_date_format='DD-MON-YY HH24.MI.SS';
SELECT
SYSTIMESTAMP raw_timestamp,
CAST(SYSTIMESTAMP AS DATE) raw_date,
TRUNC(CAST(SYSTIMESTAMP AS DATE)) trunc_date,
TRUNC(SYSTIMESTAMP) - INTERVAL '30' DAY
from dual;
RAW_TIMESTAMP RAW_DATE TRUNC_DATE TRUNC(SYSTIMESTAMP
-------------------------------------- ------------------ ------------------ ------------------
25-JUN-20 12.27.21.756299000 PM -04:00 25-JUN-20 12.27.21 25-JUN-20 00.00.00 26-MAY-20 00.00.00
For identifying users that have only logged in once, try this:
WITH user_logins as (
SELECT USER_ID,
COUNT(*) LOGIN_COUNT
FROM logins
WHERE TRUNC(LOGIN_TIMESTAMP) > TRUNC(SYSTIMESTAMP - INTERVAL '30' DAY)
GROUP BY USER_ID)
SELECT user_id, login_count
from user_logins
where login_count=1
order by user_id;

Answer 2

Please use below query, since you have string value PM in the date, you cannot use cast function, instead you have to use to_date and convert to date format.
SELECT
to_date(LOGIN_TIMESTAMP, 'DD-MON-YYYY hh.mi.ss PM'),
COUNT(DISTINCT USER_ID)
FROM
logins
WHERE
LOGIN_TIMESTAMP >= SYSDATE - 30
GROUP BY
to_date(LOGIN_TIMESTAMP, 'DD-MON-YYYY hh.mi.ss PM');