Create and execure a dynamic query

Question

hi all,
i'm trying to write a procedure in order to create a dinamyc query and calculate a certain value.
i coded something like this but it does not work:
create or replace procedure CALCOLA_OPERAZIONE
is
sql_stmt varchar2(2000);
colonna varchar2(2000);
tabella varchar2(2000);
fattore varchar2(2000);
parametro number;
bt number := 0;
cursor cur is
select cod_colonna,cod_tabella,fattore_bt from table;
begin
open cur;
    loop
        fetch cur into colonna,tabella,fattore;
        sql_stmt := 'select :1 * :2 into parametro from :3';
        EXECUTE IMMEDIATE sql_stmt USING colonna,fattore,tabella;
        bt:=bt+parametro;
    end loop;
close cur;
EXCEPTION
WHEN OTHERS THEN
      raise_application_error(-20001,'An error was encountered - '||SQLCODE||' -ERROR- '||SQLERRM);
end;here the error i get:
An error was encountered - -903 -ERROR- ORA-00903: invalid table namecan anyone help me?
Edited by: 908335 on 6-feb-2012 1.30

Answer 1

The good news is that what you want to do should be possible, but you need to take a different approach.
The bad news is that I agree with the others and think you need to take a step back and think about whether this is a good design. Dynamic SQL is a difficult solultion to implement and (within reason) static sql is almost always more maintaintable.
Still, if you're doing this as an exercise for your own knowledge or an assignment the technique is something like what I will put below (it will be untested). You will need to build the sql as text, execute it, and get the results. I prefer reference cursors for this kind of work although EXECUTE IMMEDIATE can be used. The solution will look something like (beware typos)
declare
  ref_cursor sys_refcursor;
  col           varchar2(32767);
  sql_text    varchar2(32767);
  value       varchar2(1);
begin
  col := 'dummy';
  sql_text := 'select '||col||' from dual';
  open ref_cursor using sql_text;
  fetch ref_cursor into value;
  close ref_cursor;
end;I will leave it up to you to figure out how to adapt what you have to work like this :)