Create email notification request link function - oracle

Question

I created a function to create link but am encountering errors when creating a variable, tried declaring but declare would have an error
create or replace FUNCTION CREATE_REQUEST_LINK(request_id IN VARCHAR2, task_id IN VARCHAR2)
RETURN VARCHAR2 AS
request_link varchar2(100);
BEGIN
first_half varchar2 := apex_mail.get_instance_url;
second_half varchar2 := 'f?p=&APP_ID.:&APP_PAGE.:&APP_SESSION.::::';
request_link := first_half + second_half;
RETURN request_link;
END WF_CREATE_REQUEST_LINK;
It was returning on Line 8 and 9
Error: PLS-00103: Encountered the symbol "VARCHAR2" when expecting one of the following: := . ( # % ; The symbol "." was substituted for "VARCHAR2" to continue.
Is there a way to fix. I'm kinda new to Oracle Apex
Additional question, am I right in creating the 2nd half, the plan is that the $APP_SESSION. after clicking the link will be changed into the session id after logging in.

Answer 1

You seem to want to declare two local variables first_half and second_half. Variable declarations need to happen in the declaration section of a block.
When you declare a varchar2 variable, you need to provide a length. I'll guess that you want both local variables to have a maximum length of 100.
The string concatenation operator is || not +
So you probably want something like
create or replace FUNCTION CREATE_REQUEST_LINK(
request_id IN VARCHAR2,
task_id IN VARCHAR2)
RETURN VARCHAR2
AS
request_link varchar2(100);
first_half varchar2(100) := apex_mail.get_instance_url;
second_half varchar2(100) := 'f?p=&APP_ID.:&APP_PAGE.:&APP_SESSION.::::';
BEGIN
request_link := first_half || second_half;
RETURN request_link;
END WF_CREATE_REQUEST_LINK;