MySQL 8.0

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CREATE TABLE IF NOT EXISTS  grade_point (
    id VARCHAR(5),
    grade VARCHAR(2),
    grade_value NUMERIC(2 , 1)
);
CREATE TABLE IF NOT EXISTS takes (
    id VARCHAR(5),
    grade VARCHAR(2)
);
INSERT INTO takes VALUES ("1","A"),("2","B"),("3","A"),("4","B")
CREATE PROCEDURE update_grade_point (

)
BEGIN
	DECLARE finished INTEGER DEFAULT 0;
	DECLARE _grade varchar(2) DEFAULT "";
	DECLARE _id varchar(5) DEFAULT "";

	-- declare cursor for employee email
	DEClARE curtakes 
		CURSOR FOR 
			SELECT id,grade FROM takes;

	-- declare NOT FOUND handler
	DECLARE CONTINUE HANDLER 
        FOR NOT FOUND SET finished = 1;

	OPEN curtakes;

	getidGrade: LOOP
		FETCH curtakes INTO _id,_grade;
		IF finished = 1 THEN 
			LEAVE getidGrade;
		END IF;
                insert into grade_point(id, grade, grade_value) VALUES (_id,_grade,        case
            when grade like 'A' then 4.0
            when grade like 'A-' then 3.7
            when grade like 'B+' then 3.3
            when grade like 'B' then 3.0
        end);
	END LOOP getidGrade;
	CLOSE curtakes;

END
CALL update_grade_point()
SELECT * FROM grade_point


id
grade
grade_value


1
A
4.0

2
B
3.0

3
A
4.0

4
B
3.0