Problem in setting Pragma Restrict References

Question

Dear all,
I've got a question on PRAGMA RESTRICT_REFERENCES. Please help. Thanks.
I've created a view "V_STUDENT" which retrieves student information. One of
columns in this view "STUD_NAME" will get the student name from a function
"F_STUDNAME". This function is placed in a package. No error occurs when compilation
of view & package. However, when I run the following command, problem occurs :
1) select STUD_CODE, STUD_NAME from V_STUDENT
group by STUD_CODE, STUD_NAME
ORA-06573: FUNCTION F_STUDNAME modifies package state, cannot be used here
I really don't know why or which statement would modify package state?
I've tried to change "PRAGMA RESTRICT_REFERENCES (F_STUDNAME, 'WNDS')" to
"PRAGMA RESTRICT_REFERENCES (F_STUDNAME, 'WNDS', 'WNPS')". Then, the above command executes
normally. No more error message. But what's the reason ?
2) select STUD_CODE, STUD_NAME from V_STUDENT
No error message when the setting is "PRAGMA RESTRICT_REFERENCES (F_STUDNAME, 'WNDS')" for
the above command. What're the differences ?
CREATE OR REPLACE VIEW V_STUDENT ( STUD_CODE, STUD_NAME, ...
) AS SELECT STUD_CODE, PKG1.F_STUDNAME(STUD_CODE) STUD_NAME, ...
FROM STUDNET ...
CREATE OR REPLACE PACKAGE PKG1 IS
FUNCTION F_STUDNAME(STUD_CODE STUDENT.STUD_CODE%TYPE) RETURN VARCHAR2;
PRAGMA RESTRICT_REFERENCES (F_STUDNAME, 'WNDS');
END;
CREATE OR REPLACE PACKAGE BODY PKG1 IS
FUNCTION F_STUDNAME(STUD_CODE STUDENT.STUD_CODE%TYPE) RETURN VARCHAR2 IS
stud_name VARCHAR2(50);
BEGIN
IF STUD_CODE IS NOT NULL THEN
SELECT STUD_FSTNAME| |' '| |STUD_LSTNAME
INTO stud_name
FROM ALL_STUDENT_NAME
WHERE ALL_STUD_CODE = STUD_CODE
ELSE
RETURN NULL;
END IF;
RETURN stud_name;
EXCEPTION
WHEN OTHERS THEN RETURN NULL;
END F_STUDNAME;
END;
Regards,
Twin

Answer 1

1. To use a function in the where/group by clause of a select statement the function must be WNDS and WNPS. As you have not explicitly stated that the function does not break the WNPS restriction the SQL engine assumes it does and so will not allow you to use it here. Add the restriction to the pragma, as you have done, and it will work.
2. To use a function in the select cluase of a select statement only WNDS needs to be declared. Since this is stated the statement will work