Oracle implicit parameter casting - why doesn't it always work? (ORA-06502 error) I have a Java (Spring) app that uses Oracle 10 as DB. Some legacy code has wrong parametrization of PL/SQL procedures. For instance, some input parameters are declared as OracleTypes.VARCHAR in Java DAO layer, while in fact they're NUMBER in PL/SQL procedure. 99% times this works without a problem (of course, if the sent data is actually a number), but sometimes I get the ORA-06502: PL/SQL: numeric or value error: character to number conversion error. 

I understand how to fix the problem, but I wonder why this occurs on some DB installations and on most it doesn't. This is of high importance for me because it's very difficult to inspect legacy code for wrong parameter types.
Interesting question - at first I would have said an overflow, but checking, that's ORA-01426 and if it wasn't a number, ORA-01722. Is it just datatype NUMBER which defaults to NUMBER(38)? 

But this can be diagnosed with a trace to see what's exactly going on. If you can identify the session, or can modify the connection code, you can do:

SQL&gt; alter session set events='6502 trace name errorstack level 12';

Session altered.

SQL&gt; create or replace function fn_add(p1 number, p2 number) return number
  2  as
  3  v1 number(1);
  4  begin
  5  v1 := p1 + p2;
  6  return v1;
  7  end;
  8  /

Function created.

SQL&gt; select fn_add('10', '1') from dual;
select fn_add('10', '1') from dual
       *
ERROR at line 1:
ORA-06502: PL/SQL: numeric or value error: number precision too large


Now looking in the tracefile:

---- Error Stack Dump -----
ORA-06502: PL/SQL: numeric or value error: number precision too large
----- Current SQL Statement for this session (sql_id=a36psfjj50bpv) -----
select fn_add('10', '1') from dual


That should at least get you started on root cause analysis. But be warned that these trace files can get very large, very quickly!