Oracle 21c

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CREATE TABLE student_score(
   totalscore  VARCHAR2(400) ,
   score_desc  VARCHAR2(400)
);
BEGIN
 INSERT INTO student_score VALUES ('HN_50','Higher');
 INSERT INTO student_score VALUES ('LN_51','Lower');
END;
/
1 rows affected

SELECT REGEXP_SUBSTR(totalscore, '[^_]+') AS highlow ,
       REGEXP_SUBSTR(totalscore, '[^_]+$') AS score,
       score_desc
  FROM student_score
WHERE REGEXP_LIKE(totalscore,'^HN_|^LN_')


HIGHLOW
SCORE
SCORE_DESC


HN
50
Higher

LN
51
Lower