SQL Server 2019

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SELECT 'JACK' AS PERSON, '2021-01-02' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP
INTO #TEMP 
UNION 
SELECT 'JACK' AS PERSON, '2021-01-21' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP UNION 
SELECT 'JACK' AS PERSON, '2021-01-25' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP UNION 
SELECT 'JACK' AS PERSON, '2021-02-01' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP UNION 
SELECT 'JACK' AS PERSON, '2021-02-04' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP UNION 
SELECT 'JACK' AS PERSON, '2021-02-21' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP UNION 
SELECT 'JACK' AS PERSON, '2021-03-01' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP UNION 
SELECT 'JACK' AS PERSON, '2021-03-12' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP UNION 
SELECT 'JACK' AS PERSON, '2021-03-30' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP UNION 
SELECT 'JACK' AS PERSON, '2021-04-10' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP UNION 
SELECT 'JACK' AS PERSON, '2021-04-16' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP UNION 
SELECT 'JILL' AS PERSON, '2021-01-20' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP UNION 
SELECT 'JILL' AS PERSON, '2021-01-22' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP UNION 
SELECT 'JILL' AS PERSON, '2021-01-26' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP UNION 
SELECT 'JILL' AS PERSON, '2021-02-18' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP UNION 
SELECT 'JILL' AS PERSON, '2021-02-23' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP UNION 
SELECT 'JILL' AS PERSON, '2021-02-28' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP UNION 
SELECT 'JILL' AS PERSON, '2021-03-08' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP UNION 
SELECT 'JILL' AS PERSON, '2021-03-26' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP UNION 
SELECT 'JILL' AS PERSON, '2021-03-30' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP UNION 
SELECT 'JILL' AS PERSON, '2021-04-20' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP UNION 
SELECT 'JILL' AS PERSON, '2021-04-30' AS RECORD_DATE, CAST(NULL AS SMALLINT) RECORD_GROUP

22 rows affected

person	record_date	leader_date	rn
JACK	2021-01-02	2021-01-02	1
JACK	2021-01-21	2021-01-02	2
JACK	2021-01-25	2021-01-02	3
JACK	2021-02-01	2021-01-02	4
JACK	2021-02-04	2021-02-04	5
JACK	2021-02-21	2021-02-04	6
JACK	2021-03-01	2021-02-04	7
JACK	2021-03-12	2021-03-12	8
JACK	2021-03-30	2021-03-12	9
JACK	2021-04-10	2021-03-12	10
JACK	2021-04-16	2021-04-16	11
JILL	2021-01-20	2021-01-20	1
JILL	2021-01-22	2021-01-20	2
JILL	2021-01-26	2021-01-20	3
JILL	2021-02-18	2021-01-20	4
JILL	2021-02-23	2021-02-23	5
JILL	2021-02-28	2021-02-23	6
JILL	2021-03-08	2021-02-23	7
JILL	2021-03-26	2021-03-26	8
JILL	2021-03-30	2021-03-26	9
JILL	2021-04-20	2021-03-26	10
JILL	2021-04-30	2021-04-30	11