Oracle 18c

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create table z(
a number GENERATED ALWAYS AS IDENTITY primary key ,
b numeric(7,2),
c numeric(7,2)
);

insert into z (b,c) values(0,20);
1 rows affected

insert into z (b,c) values(0,10);
1 rows affected

insert into z (b,c) values(0,40);
1 rows affected

insert into z (b,c) values(0,80);
1 rows affected

update z 
set b = c / (SELECT max(c) FROM z) * 100;
4 rows affected

SELECT
    *
FROM
    z


A
B
C


1
25
20

2
12.5
10

3
50
40

4
100
80