MySQL 8.0

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create table studs(
st_id int primary key auto_increment,
st_name varchar(30),
st_surname varchar(30),
st_course int,
st_speciality enum('km', 'webs', 'mobile', 'mech'),
st_form enum('free', 'not free'),
st_value float
);

create table activities(
activity_id int primary key auto_increment,
activity_name varchar(50),
activity_description varchar(200),
activity_date date,
activity_place varchar(50),
activity_organizer varchar(30)
);

create table participation(
participation_id int primary key auto_increment,
student_id int,
activity_id int,
participation_role varchar(20),
participation_result varchar(50),

constraint ref_studs_to_participation foreign key (student_id) references studs (st_id),
constraint ref_activities_to_participation foreign key (activity_id) references activities (activity_id)
);
INSERT INTO studs VALUES(NULL ,'testA','testB',1,'km','free', 1.6);
INSERT INTO studs VALUES(NULL ,'testA1','testB1',2,'km','free', 1.1);
INSERT INTO studs VALUES(NULL ,'testA2','testB2',3,'km','free', 1.1);


INSERT INTO activities VALUEs (NULL,'test1','test2', NOW(),'test4','test5');
INSERT INTO activities VALUEs (NULL,'test11','test21', NOW(),'test41','test51');
INSERT INTO activities VALUEs (NULL,'test12','test22', NOW(),'test42','test52');
INSERT INTO participation VALUES (NULL,1,1,'test','test');
INSERT INTO participation VALUES (NULL,1,2,'test','test');
INSERT INTO participation VALUES (NULL,1,3,'test','test');
INSERT INTO participation VALUES (NULL,2,1,'test','test');
INSERT INTO participation VALUES (NULL,2,2,'test','test');
INSERT INTO participation VALUES (NULL,3,3,'test','test');
INSERT INTO participation VALUES (NULL,3,2,'test','test');
INSERT INTO participation VALUES (NULL,3,3,'test','test');
create procedure update_st_value_by_participation(in p_how_much int)
begin

    declare p_student_id, p_value_multiplier int;
    declare is_end int default 0;
    
    declare students_cursor cursor for 
     select student_id, count(student_id) as st_participations 
    from participation group by student_id;
    
    declare continue handler for not found set is_end=1;
    
    open students_cursor;
        curs: Loop
            fetch students_cursor into p_student_id, p_value_multiplier;
            
            if is_end then
                leave curs;
            end if;
            update studs
            set st_value = st_value + p_how_much * (p_value_multiplier - 1)
            where st_id = p_student_id;
        end loop curs;
    
    close students_cursor;
end
CALL update_st_value_by_participation(21)
SELECT * FROM studs


st_id
st_name
st_surname
st_course
st_speciality
st_form
st_value


1
testA
testB
1
km
free
43.6

2
testA1
testB1
2
km
free
22.1

3
testA2
testB2
3
km
free
43.1
st_id	st_name	st_surname	st_course	st_speciality	st_form	st_value
1	testA	testB	1	km	free	43.6
2	testA1	testB1	2	km	free	22.1
3	testA2	testB2	3	km	free	43.1