Oracle SQL Developer PL/SQL return an array - oracle

Question

Devs,
I've searched everywhere I can, but I could not find solution to this simple problem.
Situation:
I need to write a procedure where it takes a column name as the input and return all the distinct values present in that column as output. And then I have to use this procedure in some c# code.
In MS server, it is very easy as it will directly give the set of results unlike in PL/SQL.
Script I could write (which is not giving me the result I need):
CREATE OR REPLACE
PROCEDURE GetCol(PARAM IN STRING, recordset OUT sys_refcursor)
AS
BEGIN
OPEN recordset FOR
SELECT DISTINCT(PARAM)
FROM my_table;
END
;
When I try to check the data in the recordset using this code:
DECLARE
l_cursor SYS_REFCURSOR;
l_sname VARCHAR2(50);
BEGIN
GetCol('col_name',l_cursor);
LOOP
FETCH l_cursor INTO l_sname;
EXIT WHEN l_cursor%NOTFOUND;
DBMS_OUTPUT.PUT_LINE(l_sname);
END LOOP;
CLOSE
Can someone help me with this code please.

Answer 1

You can also open a ref_cursor for a string value. Please take a look at this:
CREATE OR REPLACE PROCEDURE GetCol(PARAM IN VARCHAR2, recordset OUT sys_refcursor)
AS
QRY varchar2(100);
BEGIN
QRY := 'SELECT DISTINCT '||PARAM||' FROM my_table';
OPEN recordset FOR QRY;
END;
Then:
DECLARE
l_cursor SYS_REFCURSOR;
l_sname VARCHAR2(50);
BEGIN
GetCol('col_name',l_cursor);
LOOP
FETCH l_cursor INTO l_sname;
EXIT WHEN l_cursor%NOTFOUND;
DBMS_OUTPUT.PUT_LINE(l_sname);
END LOOP;
END;

Answer 2

Your problem is caused by ambiguity about what PARAM is in the procedure's SELECT statement:
CREATE OR REPLACE
PROCEDURE GetCol(PARAM IN STRING, recordset OUT sys_refcursor)
AS
BEGIN
OPEN recordset FOR
SELECT DISTINCT(PARAM) -- Ambiguity here
FROM my_table;
END;
Does PARAM refer to the table column or to the first parameter of the procedure? Oracle has assumed the parameter. You can explicitly say which like this:
SELECT DISTINCT(my_table.PARAM)
FROM my_table;
You could if appropriate (it probably isn't here) specify the procedure parameter instead:
SELECT DISTINCT(GetCol.PARAM)
FROM my_table;
Generally this is best avoided by:
always using table aliases in column references select statements, and
having a standard for parameter names that makes them less likely to clash e.g. P_PARAM.