TOO_MANY_ROWS leaves variable in indeterminate state - Is this a bug?

Question

Hello all,
Please see below that despite the handled exception, PL/SQL still alters the coontents of the variable. - I cannot reply on its initial state if there is a possibility of a TMR exception ..... it seems.
SQL> select * from v$version;
BANNER
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod
PL/SQL Release 10.2.0.1.0 - Production
CORE 10.2.0.1.0 Production
TNS for 32-bit Windows: Version 10.2.0.1.0 - Production
NLSRTL Version 10.2.0.1.0 - Production
5 rows selected.
SQL> -- Is this a problem ????
SQL>
SQL> set serveroutput on
SQL>
SQL> create table tab1(col1 varchar2(12) );
Table created.
SQL>
SQL> insert into tab1 values ('A');
1 row created.
SQL> insert into tab1 values ('B');
1 row created.
SQL> insert into tab1 values ('A');
1 row created.
SQL>
SQL> select * from tab1;
COL1
A
B
A
3 rows selected.
SQL>
SQL> declare
2 l_var varchar2(12) := 'Y'; -- initialise
3 begin
4
5 dbms_output.put_line('Initialise l_var: '||l_var);
6
7 select col1
8 into l_var
9 from tab1
10 where col1 = 'A';
11
12 dbms_output.put_line('Never get here - l_var: '||l_var);
13
14 exception
15 when TOO_MANY_ROWS then
16 dbms_output.put_line('What am i now? l_var: '||l_var);
17 end;
18 /
Initialise l_var: Y
What am i now? l_var: A
PL/SQL procedure successfully completed.
SQL>
SQL>
SQL> drop table tab1;
Table dropped.
SQL>
If you would like to try this yourself, cut from here ....
-- Is this a problem ????
set serveroutput on
create table tab1(col1 varchar2(12) );
insert into tab1 values ('A');
insert into tab1 values ('B');
insert into tab1 values ('A');
select * from tab1;
declare
l_var varchar2(12) := 'Y'; -- initialise
begin
dbms_output.put_line('Initialise l_var: '||l_var);
select col1
into l_var
from tab1
where col1 = 'A';
dbms_output.put_line('Never get here - l_var: '||l_var);
exception
when TOO_MANY_ROWS then
dbms_output.put_line('What am i now? l_var: '||l_var);
end;
drop table tab1;

Answer 1

I presume you are talking of "right" in a moral sense, rather than any other sense. An nice philosophical point.
Look at it this way. In the old days, Oracle wiped the variable whenever a TOO_MANY_ROWS exception was raised. This is "clean" but sometimes people might want to know the previously fetched value. Hence the change in Oracle 8. If you don't want to know the value, then just ignore it in the exception handler.
The only scenario it which I can see this being a potential problem is when you're fetching into an OUT parameter.. This is of course A Bad Thing and as it happens Oracle seems to save us from ourselves (at least in 9.2.0.6)...
SQL> set serveroutput on
SQL> var n number
SQL> create or replace procedure get_emp_sal (p_name in varchar2, p_sal out number)
  2  as
  3     l emp.sal%type;
  4  begin
  5       select sal into l
  6      from emp
  7      where ename = p_name;
  8      p_sal := l;
  9  exception
10      when too_many_rows then dbms_output.put_line('l='||l);
11  end;
12  /
Procedure created.
SQL> exec get_emp_sal ('VAN WIJK', :n)
l=1250
PL/SQL procedure successfully completed.
SQL> print n
         N
SQL>  create or replace procedure get_emp_sal (p_name in varchar2, p_sal out number)
  2  as
  3     l emp.sal%type;
  4  begin
  5      select sal into p_sal
  6      from emp
  7      where ename = p_name;
  8  exception
  9      when too_many_rows then dbms_output.put_line('l='||l);
10  end;
11  /
Procedure created.
SQL>  exec get_emp_sal ('VAN WIJK', :n)
l=
PL/SQL procedure successfully completed.
SQL>  print n
         N
SQL> Cheers, APC