ORA-04091 (table string.string is mutating) and Function-Based Index

Question

I've encountered a problem with DELETEing from a table when that table has a function-based index on it. The following demonstrates this:
SQL> CREATE OR REPLACE FUNCTION get_employee_location(p_empno IN number)
  2  RETURN varchar2
  3  DETERMINISTIC
  4  IS
  5  l_return_value   varchar2(20);
  6  BEGIN
  7  SELECT loc
  8  INTO   l_return_value
  9  FROM   dept
10  WHERE  deptno = (SELECT
11                   e.deptno
12                   FROM emp e
13                   WHERE empno = p_empno);
14  return l_return_value;
15  end;
16  /
Function created.
SQL> create index location_idx on emp (get_employee_location(empno));
Index created.
SQL> delete from emp;
delete from emp
ERROR at line 1:
ORA-04091: table SCOTT.EMP is mutating, trigger/function may not see it
ORA-06512: at "SCOTT.GET_EMPLOYEE_LOCATION", line 7------------------------------------------------
The question is: How can I successfully DELETE FROM emp but keep my function-based index in place?
Thanks
Andy

Answer 1

'Being able to' is 'being able to', but
it is dangerous to declare "DETERMINISTIC" for non-deterministic function.
The following problem happens on non-deterministic function index.
SQL> update dept set loc = 'NEWYORK' where deptno=10;
1 row updated.
SQL> commit;
Commit complete.
SQL> select * from emp where get_employee_location(deptno)='NEWYORK';
no rows selected
SQL> select * from dept;
    DEPTNO DNAME          LOC
        10 ACCOUNTING     NEWYORK
        20 RESEARCH       DALLAS
        30 SALES          CHICAGO
        40 OPERATIONS     BOSTON
SQL> select empno,ename from emp where get_employee_location(deptno)='NEW YORK';
     EMPNO ENAME
      7782 CLARK
      7839 KING
      7934 MILLER
SQL> select empno,ename,get_employee_location(deptno) from emp where deptno=10;
     EMPNO ENAME      GET_EMPLOYEE_LOCATION(DEPTNO)
      7782 CLARK
      7839 KING
      7934 MILLER
SQL> select empno,ename,get_employee_location(deptno) from emp where get_employee_location(deptno)='NEW YORK';
     EMPNO ENAME      GET_EMPLOYEE_LOCATION(DEPTNO)
      7782 CLARK      NEW YORK
      7839 KING       NEW YORK
      7934 MILLER     NEW YORK
SQL> drop index location_idx ;
Index dropped.
SQL> select empno,ename from emp where get_employee_location(deptno)='NEW YORK';
no rows selected