Oracle 21c

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CREATE TABLE table_name (record_id, department, "USER", login_date) AS
SELECT 1, 'IT',      'xujk', DATE '2022-01-10' + INTERVAL '10' HOUR FROM DUAL UNION ALL
SELECT 2, 'IT',      'jkl',  DATE '2022-01-10' + INTERVAL '15' HOUR FROM DUAL UNION ALL
SELECT 3, 'IT',      'xujk', DATE '2022-01-12' + INTERVAL '11' HOUR FROM DUAL UNION ALL
SELECT 4, 'FINANCE', 'mno',  DATE '2022-01-10' + INTERVAL '01' HOUR FROM DUAL UNION ALL
SELECT 5, 'FINANCE', 'abc',  DATE '2022-01-12' + INTERVAL '15' HOUR FROM DUAL UNION ALL
SELECT 6, 'FINANCE', 'def',  DATE '2022-01-12' + INTERVAL '20' HOUR FROM DUAL;
6 rows affected

SELECT *
FROM   table_name
MATCH_RECOGNIZE (
  PARTITION BY department
  ORDER     BY login_date
  ALL ROWS PER MATCH
  PATTERN (first_row {- within_18_hours* -} )
  DEFINE
    within_18_hours AS login_date <= first_row.login_date + INTERVAL '18' HOUR
)


DEPARTMENT
LOGIN_DATE
RECORD_ID
USER


FINANCE
10-JAN-22
4
mno

FINANCE
12-JAN-22
5
abc

IT
10-JAN-22
1
xujk

IT
12-JAN-22
3
xujk


SELECT *
FROM   table_name
MATCH_RECOGNIZE (
  PARTITION BY department
  ORDER     BY login_date
  ALL ROWS PER MATCH
  PATTERN (first_row {- within_18_hours* -} )
  DEFINE
    within_18_hours AS login_date <= PREV(login_date) + INTERVAL '18' HOUR
)


DEPARTMENT
LOGIN_DATE
RECORD_ID
USER


FINANCE
10-JAN-22
4
mno

FINANCE
12-JAN-22
5
abc

IT
10-JAN-22
1
xujk

IT
12-JAN-22
3
xujk

DEPARTMENT	LOGIN_DATE	RECORD_ID	USER
FINANCE	10-JAN-22	4	mno
FINANCE	12-JAN-22	5	abc
IT	10-JAN-22	1	xujk
IT	12-JAN-22	3	xujk