SQL> create unique index pk_b on b (b_num, trunc(created,'YYYY'));

Index created.

create or replace procedure calc_rating as
begin
    update
        ratings
    set
        ksi_j = dbms_random.value(- 1 , 1 )
    where
        ( 1  =  1 )
        and id in 
        (
            select
                r.id
            from
                ratings r
            where
                ( 1  =  1 )
                and exists
                (
                    select
                         1 
                    from
                        ratings r1
                    where
                        ( 1  =  1 )
                        and (r1.id = r.id)
                        and (trunc(dbms_random.value( 1 ,  7 )) =  1 )
                )
        );
end;
/
declare i number;
begin
for i in  1 .. 70000  loop
   insert into ratings (id, ksi_j)values (i, 0 );
end loop;
end;
/
begin calc_rating; end;
/
select count(*) from ratings union all select count(*) from ratings where ksi_j !=  0 ;

create table ratings (id number( 10 ) not null, ksi_j number( 10 ,  9 ) not null);

create or replace procedure calc_rating as
begin
    update ratings
    set ksi_j = dbms_random.value(- 1 ,  1 )
    where id in 
        (
        select r.id from ratings r
        where exists 
            (
            select  1  from ratings r1 
            where (r1.id = r.id) and (trunc(dbms_random.value( 1 ,  7 )) =  1 )
            )
        );
end;
/

declare i number;
begin
for i in  1 .. 70000  loop
   insert into ratings (id, ksi_j) values (i,  0 );
end loop;
end;
/

   1    select count(r.id) from ratings r where exists
   2    (
   3     select  1  from ratings r1 where (r1.id = r.id) and (trunc(dbms_random.value( 1 ,  7 )) =  1 )
   4 *  )
SQL> /

COUNT(R.ID)
 -----------
 
       11638 

SQL> /

COUNT(R.ID)
 -----------
 
       11645 

SQL> /

COUNT(R.ID)
 -----------
 
       11693 

SQL> /

COUNT(R.ID)
 -----------
 
       11563 

SQL> set autot trace exp
SQL> /


Execution Plan
 ----------------------------------------------------------
 
    0       SELECT STATEMENT Optimizer=CHOOSE
    1      0    SORT (AGGREGATE)
    2      1      FILTER
    3      2        TABLE ACCESS (FULL) OF 'RATINGS'
    4      2        FILTER
    5      4          INDEX (UNIQUE SCAN) OF 'SSS' (UNIQUE)

SQL> alter table ratings drop constraint sss;

Table altered.

SQL> select...

Execution Plan
 ----------------------------------------------------------
 
    0       SELECT STATEMENT Optimizer=CHOOSE
    1      0    SORT (AGGREGATE)
    2      1      FILTER
    3      2        TABLE ACCESS (FULL) OF 'RATINGS'
    4      2        FILTER
    5      4          TABLE ACCESS (FULL) OF 'RATINGS'

alter table ratings add constraint sss primary key(id);