Oracle Function To Return List - oracle

Question

I'm trying to develop a PLSQL function that outputs a list of employee names that I can then run through another script. I can't quite get it right though. I'm fairly new to PLSQL and am primarily used to building functions in Python, so I may be thinking about this the wrong way. At the end of all of this, I'd like to use the output of this within another script I'm writing.
Baseline Script:
SELECT EMPLOYEE FROM (
SELECT ID, EMPLOYEE, ROLE, STARTDATE,
ROW_NUMBER() OVER (PARTITION BY EMPLOYEE ORDER BY STARTDATE DESC, ID DESC) RN
FROM (
SELECT DISTINCT E.EMPLOYEE EMPLOYEE,
E.ID ID,
LR.DESCRIPTION ROLE,
ROLE_START_DATE STARTDATE
FROM EMPLOYEES E
JOIN ROLES R ON E.EMPLOYEE_ID = R.EMPLOYEE_ID
JOIN LU_ROLES LR ON R.ROLE_ID = LR.ROLE_ID
WHERE ROLE_START_DATE <= DATE '2017-12-03'))
WHERE RN = 1
My attempt at writing a PLSQL function:
CREATE FUNCTION get_employees(EMPLOYEE IN VARCHAR2)
RETURN VARCHAR2
IS EMPLOYEE_LIST;
BEGIN
SELECT EMPLOYEE FROM (
SELECT ID, EMPLOYEE, ROLE, STARTDATE,
ROW_NUMBER() OVER (PARTITION BY EMPLOYEE ORDER BY STARTDATE DESC, ID DESC) RN
FROM (
SELECT DISTINCT E.EMPLOYEE EMPLOYEE,
E.ID ID,
LR.DESCRIPTION ROLE,
ROLE_START_DATE STARTDATE
FROM EMPLOYEES E
JOIN ROLES R ON E.EMPLOYEE_ID = R.EMPLOYEE_ID
JOIN LU_ROLES LR ON R.ROLE_ID = LR.ROLE_ID
WHERE ROLE_START_DATE <= DATE '2017-12-03'))
WHERE RN = 1
RETURN EMPLOYEE_LIST
END;
I know I'm missing some syntax, I just don't know what and why...I'm reading through the docs at the moment to try to understand this. Any help you all could provide would be much appreciated!
Thanks!

Answer 1

Without your tables or sample data this has to be a bit of a guess, but a "fixed" version might be something like this:
create or replace type short_string_tt as table of varchar2(100)
/
create or replace function get_employees
( p_role_date_cutoff roles.role_start_date%type )
return short_string_tt
as
l_employee_list short_string_tt;
begin
select employee bulk collect into l_employee_list
from ( select employee
, row_number() over(partition by employee order by role_start_date desc, id desc) rn
from ( select distinct e.employee, e.id, lr.description, role_start_date
from employees e
join roles r
on r.employee_id = e.id
join lu_roles lr
on lr.role_id = r.role_id
where role_start_date <= p_role_date_cutoff )
)
where rn = 1;
return l_employee_list;
end;
/
If the number of rows returned is likely to be significant then you might look at making it a pipelined function, as these stream rows back as they are fetched rather than building the entire collection in memory before returning anything.

Answer 2

try this would it work ?
CREATE FUNCTION get_employees(EMPLOYEE IN VARCHAR2)
RETURN VARCHAR2
IS EMPLOYEE_LIST VARCHAR2(200);
BEGIN
SELECT EMPLOYEE into EMPLOYEE_LIST FROM (
SELECT ID, EMPLOYEE, ROLE, STARTDATE,
ROW_NUMBER() OVER (PARTITION BY EMPLOYEE ORDER BY STARTDATE DESC, ID DESC) RN
FROM (
SELECT DISTINCT EMPLOYEE EMPLOYEE,
E.ID ID,
LR.DESCRIPTION ROLE,
ROLE_START_DATE STARTDATE
FROM EMPLOYEES E
JOIN ROLES R ON E.EMPLOYEE_ID = R.EMPLOYEE_ID
JOIN LU_ROLES LR ON R.ROLE_ID = LR.ROLE_ID
WHERE ROLE_START_DATE <= DATE '2017-12-03'))
WHERE RN = 1;
RETURN EMPLOYEE_LIST;
END;