converting a plsql code into a function - oracle

Question

I have this piece of code which I want to convert into a function , and call the function in a select statement by passing vendor_site_id from ap_supplier_sites_all. so that I can get the value of vendor_number i.e segment1 of ap_suppliers . here in this piece of code , I have a login to fetch first 6 digits from the column attribute52 of DFF table gecm_dff_ext .
DECLARE
v_ret_val VARCHAR2(30);
v_sup_gsl VARCHAR2(30);
v_vendor_id NUMBER;
BEGIN
v_vendor_id := '${PO.H_VENDOR_ID}';--> vendor_id column from ap_suppliers
IF <condition> = 'Y'
THEN
BEGIN
SELECT SUBSTR(ATTRIBUTE52,1,6)
INTO v_sup_gsl
FROM gecm_dff_ext
WHERE primary_table ='AP_SUPPLIER_SITES_ALL'
AND primary_key = '${PO.H_VENDOR_SITE_ID}';--> This value should be vendor_site_id from ap_supplier_sites_all table
EXCEPTION
WHEN OTHERS THEN
v_sup_gsl := NULL;
END;
BEGIN
IF v_sup_gsl IS NOT NULL THEN
SELECT segment1
INTO v_ret_val
FROM ap_suppliers
WHERE segment1 = v_sup_gsl;
END IF;
EXCEPTION
WHEN OTHERS THEN
v_ret_val := '';
END;
END IF;
IF v_sup_gsl IS NULL THEN
BEGIN
SELECT SEGMENT1
INTO v_ret_val
FROM ap_suppliers
WHERE vendor_id=v_vendor_id;
EXCEPTION
WHEN OTHERS THEN
v_ret_val := '';
END;
END IF;
:return_value:=v_ret_val;
END;

Answer 1

This is a simplified example: the following SELECT returns department name for a certain department number:
SQL> select dname
2 from dept
3 where deptno = &par_deptno;
Enter value for par_deptno: 10
DNAME
--------------
ACCOUNTING
SQL>
So, how to convert it to a function? By using a proper syntax, declaring a return variable, fetching into it and - returning the result:
SQL> create or replace function f_test (par_deptno in dept.deptno%type)
2 return dept.dname%type
3 is
4 retval dept.dname%type;
5 begin
6 select dname
7 into retval
8 from dept
9 where deptno = par_deptno;
10
11 return retval;
12 exception
13 when no_data_found then
14 return null;
15 end;
16 /
Function created.
SQL> select f_test(10) from dual;
F_TEST(10)
---------------------------------------------------------------------------
ACCOUNTING
SQL> select f_test(999) from dual;
F_TEST(999)
---------------------------------------------------------------------------
SQL>
This is what you should do. It seems that you are returning the v_ret_val, so - your code might look like this:
create or replace function f_test (par_vendor_id po.h_vendor_id%type)
return ap_suppliers.segment1%type
is
v_ret_val ap_suppliers.segment1%type;
begin
if <condition> = 'Y' then
...
end if;
return v_ret_val;
end;