Need help for dynamic calculation in oracle sql query - sql

Question

I Have a table tab_1 with below values.
ID Calculation value
1 10
2 10
3 1+2
4 5
5 3-2
6 5+1
Need help writing the query for following logic. I have a table where the records contain either calculation strings or values to be used in calculations. I need to parse the calculation like this:
ID 3 is the sum of ID 1 and 2.
ID 5 is the minus of ID 3 and 2.
ID 6 is the sum of ID 5 and 1.
Then I need to select the records for the referenced IDs and perform the calculations. My
expected output:
ID Calculation value
3 1+2 20
5 3-2 10
6 5+1 20
Thanks -- nani

Answer 1

"Need help writing the query for below logic."
This is not a problem which can be solved in pure SQL, because:
executing the calculation string requires dynamic SQL
you need recursion to look up records and evaluate the results
Here is a recursive function which produces the answers you expect. It has three private procs so that the main body of the function is simple to understand. In pseudo-code:
look up record
if record is value then return it and exit
else explode calculation
recurse 1, 3, 4 for each part of exploded calculation until 2
Apologies for the need to scroll:
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;
/
Run like this:
SQL> select dyn_calc(6) from dual;
DYN_CALC(6)
-----------
20
SQL>
or, to get the output exactly as you require:
select id, calculation, dyn_calc(id) as value
from t23
where calculation is not null;
Notes
There is no exception handling. If the data is invalid the function will just blow up
the split_calc() proc uses translate() to extract the operator rather than regex. This is because regexp_substr(p_calc, '[\-\+\*\%]', 1, 1) mysteriously swallows the -. This appears to be an environment-related bug. Consequently extending this function to process 1+4+2 will be awkward.
Here is a LiveSQL demo.

Answer 2

In SQL:
select 'ID ' +ID+ ' is the ' + case when calculation like '%-%' then ' minus '
when calculation like '%+%' then ' sum ' END +' of
ID'+replace(replace(calculation,'+',' and '),'-',' and ')
from tab_1
where calculation is not null
In Oracle:
select 'ID ' ||ID|| ' is the ' || case when calculation like '%-%' then ' minus '
when calculation like '%+%' then ' sum ' END|| ' of
ID'||replace(replace(calculation,'+',' and '),'-',' and ')
from tab_1
where calculation is not null