drop  table t23 

create table t23 (ID number, Calculation varchar2(128), value number)

insert into t23 values (1, null,10)

insert into t23 values (2, null,10)

insert into t23 values (3,'1+2',null)

insert into t23 values (4, null,5)

insert into t23 values (5,'3-2',null)

insert into t23 values (6,'5+1',null)

alter table t23 add constraint t23_pk primary key (id)

select regexp_substr(calculation, '[0-9]+', 1, 1) as n1 
       , regexp_substr(calculation, '[\-\+\*\%]', 1, 1) as oprtr 
       , regexp_substr(calculation, '[0-9]+', 1, 2) as n2 
from t23 
where calculation is not null 

create or replace function dyn_calc 
     (p_id in number) 
      return number 
is  
    result number; 
    n1 number; 
    n2 number; 
    l_rec t23%rowtype; 
    l_val number; 
     
    type split_calc_r is record ( 
        val1 number 
        , operator varchar2(1) 
        , val2 number 
    ); 
    l_calc_rec split_calc_r; 
     
    function get_rec 
        (p_id in number) 
        return t23%rowtype 
    is  
        rv t23%rowtype; 
    begin 
        select * 
        into rv    
        from t23 
        where id = p_id; 
        return rv; 
    end get_rec;     
 
     
    procedure split_calc 
       (p_calc in varchar2 
        , p_n1 out number 
        , p_n2 out number 
        , p_operator out varchar2) 
    is 
    begin 
         p_n1 := regexp_substr(p_calc, '[0-9]+', 1, 1); 
         p_n2 := regexp_substr(p_calc, '[0-9]+', 1, 2); 
         p_operator := translate(p_calc, '-+*%01923456789','-+*%'); --regexp_substr(p_calc, '[\-\+\*\%]', 1, 1); 
    end split_calc; 
 
    function exec_calc  
        (p_n1 in number 
          , p_n2 in number 
          , p_operator in varchar2) 
        return number 
    is  
        rv number; 
    begin 
        execute immediate 
            'select :n1 ' ||  p_operator ||  ' :n2 from dual' 
            into rv 
            using p_n1, p_n2;  
        return rv; 
    end exec_calc;     
 
     
begin 
    l_rec := get_rec(p_id); 
 
    if l_rec.value is not null then 
        result := l_rec.value; 
    else         
         split_calc(l_rec.calculation 
                     , l_calc_rec.val1 
                     , l_calc_rec.val2 
                     , l_calc_rec.operator); 
         n1 := dyn_calc (l_calc_rec.val1); 
         n2 := dyn_calc (l_calc_rec.val2); 
         result := exec_calc(n1, n2, l_calc_rec.operator); 
    end if; 
     
    return result; 
end; 

select id, calculation, dyn_calc(id) as value 
from t23 
where calculation is not null