cannot perform DML operation inside a query - sql

Question

I cannot convince why I can't add DML operation inside Oracle Function especially inside cursor loop. I feel Oracle don't support DML operation inside cursor loop.
How can I do If I need to insert into table inside cursor loop? Create new store procedure inside it or something else?
Error Message : cannot perform DML operation inside a query
Here is my function,
CREATE OR REPLACE FUNCTION TEST_FUNC(U_ID IN VARCHAR2)
RETURN VARCHAR2
IS
V_MESSAGE VARCHAR2(30);
CURSOR C_PERSON (V_ID VARCHAR2) IS
SELECT NAME_UPPER
FROM TBL_PERSON
WHERE NAME_UPPER = V_ID;
BEGIN
FOR C_PERSON_CURSOR IN C_PERSON(U_ID)
LOOP
INSERT INTO TMP_PERSON(NAME) VALUES (C_PERSON_CURSOR.NAME_UPPER);
END LOOP;
RETURN V_MESSAGE;
EXCEPTION
WHEN OTHERS THEN
raise_application_error(-20001,'An error was encountered - '||SQLCODE||' -ERROR- '||SQLERRM);
END;

Answer 1

You can use DML inside a PL/SQL function - no problem. However, the function can only be called from PL/SQL, not from SQL - i.e. it can be called like this:
declare
l_message varchar2(30);
begin
l_message := test_func('123');
end;
... but not like this:
select test_func(empno) from emp;
That leads to the error message you posted.
Many people (including me) don't like functions that have "side effects" like this, but that is a matter of best practice and standards, not a technical issue.

Answer 2

You can perform DML operations inside an Oracle PL/SQL function and, although this is generally not a good practice, call it from SQL. The function has to be marked with a pragma AUTONOMOUS_TRANSACTION and the transaction has to be committed or rolled back before exiting the function (see AUTONOMOUS_TRANSACTION Pragma).
You should be aware that this kind of function called from SQL can dramatically degrade your queries performances. I recommend you use it only for audit purposes.
Here is an example script starting from your function:
CREATE TABLE TBL_PERSON (NAME_UPPER VARCHAR2(30));
CREATE TABLE TMP_PERSON (NAME VARCHAR2(30));
INSERT INTO TBL_PERSON (NAME_UPPER) VALUES ('KING');
CREATE OR REPLACE FUNCTION TEST_FUNC(U_ID IN VARCHAR2)
RETURN VARCHAR2
IS
PRAGMA AUTONOMOUS_TRANSACTION; -- Needed to be called from SQL
V_MESSAGE VARCHAR2(2000);
CURSOR C_PERSON (V_ID VARCHAR2) IS
SELECT NAME_UPPER
FROM TBL_PERSON
WHERE NAME_UPPER = V_ID;
BEGIN
FOR C_PERSON_CURSOR IN C_PERSON(U_ID)
LOOP
INSERT INTO TMP_PERSON(NAME) VALUES (C_PERSON_CURSOR.NAME_UPPER);
V_MESSAGE := SQL%ROWCOUNT
|| ' Person record successfully inserted into TMP_PERSON table';
END LOOP;
COMMIT; -- The current autonomous transaction need to be commited
-- before exiting the function.
RETURN V_MESSAGE;
EXCEPTION
WHEN OTHERS THEN
ROLLBACK;
raise_application_error(-20001,'An error was encountered - '||SQLCODE||' -ERROR- '||SQLERRM);
END;
/
PROMPT Call the TEST_FUNC function and insert a new record into TMP_PERSON table
SELECT TEST_FUNC('KING') FROM DUAL;
PROMPT Content of the TMP_PERSON table
COL NAME FOR A30
SELECT * FROM TMP_PERSON;
When running the previous script we get the following output:
Table created.
Table created.
1 row created.
Function created.
Calling the TEST_FUNC function and insert a new record into TMP_PERSON table
TEST_FUNC('KING')
------------------------------------------------------------
1 Person record successfully inserted into TMP_PERSON table
Content of the TMP_PERSON table
NAME
------------------------------
KING