Function return sys_refcursor call from sql with specific columns

Question

This may find little silly, but I would like to know whether this is possible.

I have a function which return sys_refcursor

CREATE OR REPLACE FUNCTION get_employee_details(p_emp_no IN EMP.EMPNO%TYPE)
   RETURN SYS_REFCURSOR
AS
   o_cursor   SYS_REFCURSOR;
BEGIN
   OPEN o_cursor FOR
      SELECT EMPNO,
             ENAME,
             JOB,
             MGR,
             HIREDATE,
             SAL,
             COMM,
             DEPTNO
        FROM emp
       WHERE EMPNO = p_emp_no;

   RETURN o_cursor;
 -- exception part
END;
/

and I could get the results using

select  get_employee_details('7369') from dual;

Is it possible to get the result from the above function by specifying column name? E.g. If I would want to get ename or salary, how could I specify in the sql statement without using a plsql block? Something like

select  get_employee_details('7369') <specific column> from dual;

Answer 1

For that purpose, you might want to take a look at PIPELINED functions. You will have to declare explicit type at PL/SQL level though. That part will set the output column name:

CREATE OR REPLACE TYPE my_rec AS OBJECT (
  c CHAR,
  n NUMBER(1)
);

CREATE OR REPLACE TYPE my_tbl AS TABLE OF my_rec;

Now, the great advantage is you can not only "rename" your columns, but modify the records from your cursor on the fly too. For ex:

CREATE OR REPLACE FUNCTION my_fct
RETURN my_tbl PIPELINED
AS
  -- dummy data - use your own cursor here
  CURSOR data IS
      SELECT 'a' as A, 1 AS B FROM DUAL UNION 
      SELECT 'b', 2 FROM DUAL UNION 
      SELECT 'c', 3 FROM DUAL UNION 
      SELECT 'd', 4 FROM DUAL;
BEGIN
  FOR the_row IN data
  LOOP 
      PIPE ROW(my_rec(the_row.a, the_row.b*2));
      --                                  ^^
      --                            Change data on the fly
  END LOOP;
END

Usage:

SELECT * FROM TABLE(my_fct())
--            ^^^^^^^^^^^^^^^
--     Use this "virtual" table like any
--     other table. Supporting `WHERE`  clause
--     or any other SELECT clause you want

Producing:

C   N
a   2
b   4
c   6
d   8