Oracle 18c

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CREATE TABLE table_name (tran_dt) AS
SELECT date'2021-05-06' FROM dual UNION
SELECT date'2021-05-24' FROM dual UNION
SELECT date'2021-06-25' FROM dual UNION
SELECT date'2021-07-02' FROM dual UNION
SELECT date'2021-07-27' FROM dual UNION
SELECT date'2021-08-16' FROM dual UNION
SELECT date'2021-08-23' FROM dual UNION
SELECT date'2021-10-01' FROM dual UNION
SELECT date'2021-12-31' FROM dual
9 rows affected

ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS';
SELECT tran_dt,
       alert,
       tran_dt
         - LAG(CASE alert WHEN 'Yes' THEN tran_dt END, 1, tran_dt)
             IGNORE NULLS OVER (ORDER BY tran_dt)
         AS days
FROM   table_name
MATCH_RECOGNIZE (
  ORDER BY tran_dt
  MEASURES
    CLASSIFIER() AS alert
  ALL ROWS PER MATCH
  PATTERN ( "Yes" "No"* )
  DEFINE
    "No" AS tran_dt <= "Yes".tran_dt + INTERVAL '90' DAY
)


TRAN_DT
ALERT
DAYS


2021-05-06 00:00:00
Yes
0

2021-05-24 00:00:00
No
18

2021-06-25 00:00:00
No
50

2021-07-02 00:00:00
No
57

2021-07-27 00:00:00
No
82

2021-08-16 00:00:00
Yes
102

2021-08-23 00:00:00
No
7

2021-10-01 00:00:00
No
46

2021-12-31 00:00:00
Yes
137


WITH dates (tran_dt, rn) AS (
  SELECT tran_dt,
         ROW_NUMBER() OVER (ORDER BY tran_dt) AS rn
  FROM   table_name
),
rolling_dates (tran_dt, alert, rn, days, last_alert) AS (
  SELECT tran_dt, 'Yes', rn, 0, tran_dt
  FROM   dates
  WHERE  rn = 1
UNION ALL
  SELECT d.tran_dt,
         CASE
         WHEN d.tran_dt <= r.last_alert + INTERVAL '90' DAY
         THEN 'No'
         ELSE 'Yes'
         END,
         d.rn,
         d.tran_dt - r.last_alert,
         CASE
         WHEN d.tran_dt <= r.last_alert + INTERVAL '90' DAY
         THEN r.last_alert
         ELSE d.tran_dt
         END
  FROM   rolling_dates r
         INNER JOIN dates d
         ON (r.rn + 1 = d.rn)
)
SELECT tran_dt,
       alert,
       days
FROM   rolling_dates;


TRAN_DT
ALERT
DAYS


2021-05-06 00:00:00
Yes
0

2021-05-24 00:00:00
No
18

2021-06-25 00:00:00
No
50

2021-07-02 00:00:00
No
57

2021-07-27 00:00:00
No
82

2021-08-16 00:00:00
Yes
102

2021-08-23 00:00:00
No
7

2021-10-01 00:00:00
No
46

2021-12-31 00:00:00
Yes
137

TRAN_DT	ALERT	DAYS
2021-05-06 00:00:00	Yes	0
2021-05-24 00:00:00	No	18
2021-06-25 00:00:00	No	50
2021-07-02 00:00:00	No	57
2021-07-27 00:00:00	No	82
2021-08-16 00:00:00	Yes	102
2021-08-23 00:00:00	No	7
2021-10-01 00:00:00	No	46
2021-12-31 00:00:00	Yes	137