Could you tell me why I get ORA- 903

SQL> create or replace function sumup(p_in varchar2)
  2  return number is
  3  l_out number;
  4  begin
  5  execute immediate 'select count(*) into l_out from :x' using in p_in;
  6  return l_out;
  7  end;
  8  /

Function created.

SQL> show errors
No errors.
SQL> select sumup('T_1BYTE') from dual;
select sumup('T_1BYTE') from dual
       *
ERROR at line 1:
ORA-00903: invalid table name
ORA-06512: at "USER.SUMUP", line 5
 The user 'USER' owns the table 'T-1BYTE'.

Thanks 

Hi Tom,
Could you please suggest how to approach this. I have a table with certain fields. I have to derive a data element using this table, which is calculated as a function of number of fields of tab_a, however the exact expression is stored in a look up table - tab_b.

create table tab_a
(f1 number
,f2 number
)

create table tab_b
(id number
,expr varchar2(200))

INSERT INTO TAB_A ( F1, F2 ) VALUES ( 100, 1); 
INSERT INTO TAB_A ( F1, F2 ) VALUES ( 200, 1); 
INSERT INTO TAB_A ( F1, F2 ) VALUES ( 300, 2); 
INSERT INTO TAB_A ( F1, F2 ) VALUES ( 400, 3);  


INSERT INTO TAB_B ( ID, EXPR ) VALUES (1, 'EXP(-1)F1+F2'); 
INSERT INTO TAB_B ( ID, EXPR ) VALUES ( 2, 'EXP(-1)*F1-F2'); 
INSERT INTO TAB_B ( ID, EXPR ) VALUES ( 3, 'EXP(-1)*F1-10*F2'); 
commit;

SQL> select * from tab_a;

        F1         F2
---------- ----------
       100          1
       200          1
       300          2
       400          3


select ID, expr from tab_b;

        ID
----------
EXPR
--------------------------------------------------------------------------------
         1
EXP(-1)*F1+F2

         2
EXP(-1)*F1-F2

         3
EXP(-1)*F1-10*F2

I would like to get a derived column, which will be added to tab_a, and the logic is:
if tab_a.f2  = tab_b.id then corresponding expression from tab_b will be used.



Many thanks