Create Fucntion returning Table in pl/sql - oracle

Question

TEMP table:
Node
Curr_Cnt
Prev_Cnt
Diff
First
20
40
20
Second
30
70
40
CREATE OR REPLACE FUNCTION NEW_FUNCTION
RETURNS table
IS
c_rec TEMP%ROWTYPE;
TYPE c_tab IS TABLE OF c_rec%TYPE INDEX BY PLS_INTEGER;
l_c_tab c_tab;
BEGIN
SELECT * INTO c_tab FROM
--**The below with clause starting from with returns the same table structure as above temp table**
( WITH batch_id_dtl AS
(SELECT a.*,
rownum rnum
FROM
(SELECT MIN(creation_date) min_cr,
MAX(creation_date) max_cr,
batch_id
FROM oalterr.q_audit_results
GROUP BY batch_id
ORDER BY 1 DESC
)a
WHERE BATCH_ID <= 251940
),
curr_cnt AS
......rest of the code......
);
RETURN C_TAB;
END NEW_FUNCTION;
The above function returns the following error:
expression 'C_TAB' is inappropriate as the left hand side of an assignment statement.
Can anyone please tell me what type should I add in return part and what am I doing wrong in the execution part between begin and end.

Answer 1

For sample table (the one you posted)
SQL> select * from temp;
NODE CURR_CNT PREV_CNT DIFF
------ ---------- ---------- ----------
First 20 40 20
Second 30 70 40
create type at SQL level so that function recognizes it:
SQL> create or replace type t_row as object
2 (node varchar2(10),
3 curr_cnt number,
4 prev_cnt number,
5 diff number);
6 /
Type created.
SQL> create or replace type t_tab as table of t_row;
2 /
Type created.
Function returns a type; for example, number, varchar2 or - in your case - t_tab:
SQL> create or replace function new_function
2 return t_tab
3 is
4 l_tab t_tab;
5 begin
6 select t_row(node, curr_cnt, prev_cnt, diff)
7 bulk collect
8 into l_tab
9 from temp;
10 return l_tab;
11 end new_function;
12 /
Function created.
So far so good. Now, call it. One way is straightforward, just like selecting sysdate (which is also a function):
SQL> select new_function from dual;
NEW_FUNCTION(NODE, CURR_CNT, PREV_CNT, DIFF)
--------------------------------------------------------------------------------
T_TAB(T_ROW('First', 20, 40, 20), T_ROW('Second', 30, 70, 40))
but that looks kind of ugly. Better way is
SQL> select * from table(new_function);
NODE CURR_CNT PREV_CNT DIFF
---------- ---------- ---------- ----------
First 20 40 20
Second 30 70 40
SQL>

Answer 2

The easiest way is to create the function with the PIPELINED clause and then, in body, using the native PL/SQL approach, in a loop iterate trough your select as cursor and return each row with PIPE ROW.
Aditionaly, it would be better to declare the return type and the table function in a package and to avoid generic return types.
Ofc. you then use such a function as
select * from table(package.function())
See also: https://docs.oracle.com/cd/B19306_01/appdev.102/b14289/dcitblfns.htm