Using CASE in ORDER BY

Question

Hi. I have a select statement that returns a ref cursor for a report I'm working on. My predicament is the order by depends on a parameter provided by the user. If you have any suggestions or related experience, please let me know...I would greatly appreciate it.
-- Requirement is
IF P_SORT = 1 THEN
SORT BY emp_id, emp_name, hiredate
ELSIF P_SORT = 2 THEN
SORT BY emp_name, deptno, hiredate
ELSE
SORT BY emp_id
-- Current statement
SELECT emp_id, emp_name, hiredate, sal
FROM employee
ORDER BY CASE
WHEN P_SORT = 1 THEN 'emp_id, emp_name, hiredate'
WHEN P_SORT = 2 THEN 'emp_name, deptno, hiredate'
ELSE
'emp_id'
END;
The statement is compiling but the order by is not working. I hope this is possible. I've searched here and there and I can only see order by's set with only 1 column and with the same data type as the other option.
Thank you.

Answer 1

Dynamic SQL (you don't know what the query is until runtime), so build the statement string based on the parameter value. Roughly:
v_stmt := 'select this, that, whatever into ... from wherever':
--do the if-then-else or case in PL/SQL
if 1 then v_order := ' order by this, that, whatever';
else
v_order := ' whatever, that, this';
end if;
v_stmt := v_stmt||v_order;
execute immediate v_stmt;