SQL Server 2019

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create table EVENT_NARATIVE(EventNum nvarchar(100),SEQ int,MESSAGE_TIME datetime,MESSAGE nvarchar(100));
create table GRADE_HISTORY(EventNum nvarchar(100),CHANGE_DATE datetime,GRADE int);
insert into EVENT_NARATIVE values
('000001-01012021' , 20770236  , '2021-01-01 00:03:36'  , 'CODE set to 6D02'),
('000001-01022020' ,  8339846   , '2020-02-01 00:06:14'  , 'CODE set to 17B01'),
('000001-01022021' , 22038639  , '2021-02-01 00:04:44'  , 'CODE set to 17A02');



insert into GRADE_HISTORY values
('000001-01012021' ,  '2021-01-01 00:03:15'    ,   2),
('000001-01012021' ,  '2021-01-01 00:03:37'   ,   3),
('000001-01012021' ,  '2021-01-01 00:03:40'   ,    5),
('000001-01022020' ,  '2020-02-01 00:06:10'   ,    2),
('000001-01022020' ,  '2020-02-01 00:06:15'   ,    2),
('000001-01022020'  , '2020-02-01 00:06:18'   ,   5),
('000001-01022020'   ,'2020-02-01 00:06:20'    ,   5),
('000001-01022021'   ,'2021-02-01 00:04:40'    ,   2),
('000001-01022021'  , '2021-02-01 00:04:42'    ,   3),
('000001-01022021' ,  '2021-02-01 00:04:44'    ,   0),
('000001-01022021',   '2021-02-01 00:04:54'    ,   5);
14 rows affected

SELECT EventNum,SEQ,CHANGE_DATE,GRADE
FROM
    (SELECT N.EventNum,N.SEQ,G.CHANGE_DATE,G.GRADE,ROW_NUMBER() OVER(PARTITION BY N.EventNum ORDER BY (SELECT null)) AS NUM
    FROM EVENT_NARATIVE N 
    JOIN GRADE_HISTORY G ON N.EventNum = G.EventNum
    WHERE G.CHANGE_DATE >= N.MESSAGE_TIME AND N.MESSAGE LIKE 'CODE set to%') T
WHERE NUM = 1


EventNum
SEQ
CHANGE_DATE
GRADE


000001-01012021
20770236
2021-01-01 00:03:37.000
3

000001-01022020
8339846
2020-02-01 00:06:15.000
2

000001-01022021
22038639
2021-02-01 00:04:44.000
0

EventNum	SEQ	CHANGE_DATE	GRADE
000001-01012021	20770236	2021-01-01 00:03:37.000	3
000001-01022020	8339846	2020-02-01 00:06:15.000	2
000001-01022021	22038639	2021-02-01 00:04:44.000	0