Question

When does the below sql function can cause an exception other than NO DATA FOUND?
v_ExchangeRate is of type float.The datatype of rate column is NUMBER(14, 10) and this column can not contain NULL values.

BEGIN
SELECT rate
INTO v_ExchangeRate
FROM exchange_rate
WHERE currency_code = CurrencyCode
AND status        = 'A';

The data type of exchange_rate in database is NUMBER(14,10)

Edit
Multiple rows cannot be returned by the where clause as the currency_code is the primary key.

Answer 1

Possible exceptions (not an exhaustive list by any means):

1) ORA-00942: table or view does not exist

declare
  var integer;
begin
  select 1 into var from nosuchtable;
end;

2) ORA-06502: PL/SQL: numeric or value error: character to number conversion error

declare
  var integer;
begin
  select 'x' into var from dual;
end;

3) ORA-06502: PL/SQL: numeric or value error: character string buffer too small

declare
  var varchar2(1);
begin
  select 'xx' into var from dual;
end;

4) ORA-01722: invalid number

SQL> create table t1 (n1 number);

Table created.

SQL> insert into t1 values (1);

1 row created.

SQL> declare
  2    var varchar2(1);
  3  begin
  4    select 'x' into var
  5    from t1 where n1 = 'y';
  6  end;
  7  /
declare
*
ERROR at line 1:
ORA-01722: invalid number
ORA-0512: at line 4

Can you not create a copy of the function, remove the WHEN OTHERS part, and test it in SQL Plus or an IDE to see what exception you get?