No_data_found Error when the revevant data is there - oracle10g

Question

I'm relatively new at PL/SQL so what I'm about to ask might sound somewhat elementary. I'm trying to run the following code and getting a No_Date_Found error when I shouldn't. I'm trying to execute a loop. I'm trying to select a set of values into variables based on another variable. The highlighted Bold line is where the error occurs. If I replace the v_tariff_code variable with a literal value in that line, the error doesn't occur anymore. Help please?
set serveroutput on
declare
v_remaining_arrears number := 0;
v_tariff_code date;
v_tariff_store date; --a variable that stores the value of the previous tariff while the above variable takes the next tariff code value
v_session_start_date date; --session start date
v_con_date date; --connection date
v_start_date date;
v_c_code varchar2(10);
v_cat_code number;
vunits number;
v_w_rate number;
v_s_rate number;
v_multiples number;
v_session_current varchar2(20);
v_counter number;
v_date1 date;
v_date2 date;
begin
v_c_code := 'D2203447';
v_session_current := 'JAN2014-FEB2014';
--V_SESSION_START_DATE := '01-JAN-14';
--v_date1 := v_session_start_date; --v_date1 would always begin as the session start date
--select v_session_start_date into v_date1 from dual;
--loop
select cat_code, units, con_date into v_cat_code, vunits, v_con_date from consumer where c_code = v_c_code;
select start_date into v_session_start_date from bill_session where session_code = v_session_current;
v_start_date := v_session_start_date;
loop
v_start_date := v_start_date - 30;
select MAX(tariff_code) INTO v_TARIFF_CODE from tariff where tariff_code < V_START_DATE;
**select w_rate, s_rate into v_w_rate, v_s_rate from cat_tariff where cat_code = v_cat_code and
tariff_code = v_tariff_code;**
v_remaining_arrears := v_remaining_arrears + ((round(v_w_rate *v_multiples*vunits) + round(v_s_rate * vunits)));
exit when v_start_date < v_con_date;
--DBMS_OUTPUT.PUT_LINE('ARREARS = ' || V_REMAINING_ARREARS);
end loop;
DBMS_OUTPUT.PUT_LINE('ARREARS = ' || V_REMAINING_ARREARS);
end;
Can you help?

Answer 1

select w_rate, s_rate
into v_w_rate, v_s_rate
from cat_tariff
where cat_code = v_cat_code and tariff_code = v_tariff_code;
This is an exact fetch which must return exactly one record. Is query returns zero or more then one records it causes the exception.
Try to add dbms_output.put_line(v_cat_code || ',' || v_tariff_code); before the query. Exactly before the exception this line will show problem values of v_cat_code and v_tariff_code.
Probable you wolud like to ignore this exception and process only cases which definitely return data. In this case you shold use BEGIN … EXCEPTION … END
begin
select w_rate, s_rate
into v_w_rate, v_s_rate
from cat_tariff
where cat_code = v_cat_code and tariff_code = v_tariff_code;
-- DO SOMETHING USEFULL WITH v_w_rate, v_s_rate
exception
when no_data_found then null;
when others then raise;
end;