Solution to "cannot perform a DML operation inside a query"?

Question

I am using a Data Analysis tool and the requirement I have was to accept a value from the user, pass that as a parameter and store it in a table. Pretty straighforward so I sat to write this

create or replace
procedure complex(datainput in VARCHAR2)
is
begin
insert into dumtab values (datainput);
end complex;

I executed this in SQL Developer using the following statement

begin
complex('SomeValue');  
end;

It worked fine, and the value was inserted into the table. However, the above statements are not supported in the Data Analysis tool, so I resorted to use a function instead. The following is the code of the function, it compiles.

create or replace
function supercomplex(datainput in VARCHAR2)
return varchar2
is
begin
insert into dumtab values (datainput);
return 'done';
end supercomplex;   

Once again I tried executing it in SQL Developer, but I got cannot perform a DML operation inside a query upon executing the following code

select supercomplex('somevalue') from dual;

My question is - I need a statement that can run the mentioned function in SQL Developer or - A function that can perform what I am looking for which can be executed by the select statement. - If it is not possible to do what I'm asking, I would like a reason so I can inform my manager as I am very new (like a week old?) to PL/SQL so I am not aware of the rules and syntaxes.

P.S. How I wish this was C++ or even Java :(

EDIT

I need to run the function on SQL Developer because before running it in DMine (which is the tool) in order to test if it is valid or not. Anything invalid in SQL is also invalid in DMine, but not the other way around.

Thanks for the help, I understood the situation and as to why it is illegal/not recommended

Solution 1

You could use the directive pragma autonomous_transaction. This will run the function into an independant transaction that will be able to perform DML without raising the ORA-14551.

Be aware that since the autonomous transaction is independent, the results of the DML will be commited outside of the scope of the parent transaction. In most cases that would not be an acceptable workaround.

SQL> CREATE OR REPLACE FUNCTION supercomplex(datainput IN VARCHAR2)
  2     RETURN VARCHAR2 IS
  3     PRAGMA AUTONOMOUS_TRANSACTION;
  4  BEGIN
  5     INSERT INTO dumtab VALUES (datainput);
  6     COMMIT;
  7     RETURN 'done';
  8  END supercomplex;
  9  /

Function created

SQL> SELECT supercomplex('somevalue') FROM dual;

SUPERCOMPLEX('SOMEVALUE')
--------------------------------------------------------------------------------
done

SQL> select * from dumtab;

A
--------------------------------------------------------------------------------
somevalue

Tom Kyte has a nice explanation about why the error is raised in the first place. It is not safe because it may depend upon the order in which the rows are processed. Furthermore, Oracle doesn't guarantee that the function will be executed at least once and at most once per row.

Solution 2

Just declare a variable to accept the return value, for example:

declare
    retvar varchar2(4);
begin
    retvar := supercomplex('somevalue');
end;

The select doesn't work because the function is performing an insert, if all it did was return a value then it would work.

Solution 3

Just execute the function in a dummy if ... end if; statement to ignore the return value:

exec if supercomplex('somevalue') then null; end if;

Or execute it as a parameter for put_line procedure to output the return value:

exec dbms_ouput ('result of supercomplex='||supercomplex('somevalue'));

result of supercomplex=done