Identifying the Weekday for an Order Date in PL/SQL as stored function - sql

Question

Code:
CREATE OR REPLACE FUNCTION DAY_ORD_SF
(
P_DATE_CREATED IN bb_basket.dtcreated%type
)
RETURN DATE AS
lv_date_created bb_basket.dtcreated%type;
BEGIN
SELECT to_char(to_date(P_DATE_CREATED,'yyyy-mm-dd'),'DAY') DAY_CREATED
INTO lv_date_created
FROM BB_BASKET
WHERE lv_date_created <= sysdate
ORDER BY lv_date_created ASC;
RETURN lv_date_created;
END DAY_ORD_SF;
/
SELECT IDBASKET, dtcreated date_created, to_char(DTCREATED,'DAY') DAY_CREATED, day_ord_sf(dtcreated) weekday_created
FROM BB_BASKET
order by DTCREATED asc;
This is my stored function I am working on as a task to practice stored function. I am really close to finishing this problem, but I am getting a no data found error. I'm not really understanding this error because when I run the code by itself it works. Basically this function is suppose to taking a date and return a varchar2 data type. I did have the "to_date(…,'yyyy-mm-dd'),.." gone before adding at that piece of code into the function.
First part of this task is to create a SELECT statement that lists the basket ID and weekday for every basket, and the second part of the task is to create a SELECT statement, using a GROUP BY clause to list the total number of baskets per weekday. Based on the results, what’s the most popular shopping day? Also I forgot to ask, if you can tell me why I am getting the "No data found" error that would be much appreciated!
Thanks for helping me out!

Answer 1

Well, there seems to be mutiple issues here.
Lets start with no data found problem. In case you use INTO within select statment and select returns no rows, you get an no data found exception. This can be handled via anonymouse begin end block with exception handler inside, but I believe this is not the case. As example:
declare
v_value number;
begin
select null
into v_value
from dual
where 1=2;
exception
when NO_DATA_FOUND then
null; -- Ignore exception and continue
end;
Condition 1=2 is never met and therefore the select always returns no rows, this will always produce no data found error. With exception handler we decide what to do next. Null will do nothing in this example.
Back to your function, your condition is if variable lv_date_created is less or equal to current date then do something. This will never work as lv_date_created will be at the moment of execution equal to null. It was just declared in your function and then used in your select. This will always lead to false and therefore select will always return no rows and no data found exception.
You also mentioned that you want the function to return varchar2 but your definition sais it returns date. Also variable lv_date_created is of type date and this is variable that is returned and you fill it with varchar2 value so apparently Oracle is doing some uncontroled conversion of the value of this is not throwing an exception about expected datatypes.
Also condition lv_date_created <= sysdate may indicate that select will find mutiple values and with INTO, this will cause too many rows exception if mutiple rows are found.
Now lets get to fixing this function. The main question is if you need to slect something in it or not. Selecting something like that usualy is used to check if entry in table exists and no data found exceptions would tell us that entry does not exist. If it is a general function to be used on mutiple places in your DB then I think select is not needed. I will include both solutions as example.
Note for this first one that you should no longer provide dtcreated colume on calling it but idbasket.
CREATE OR REPLACE FUNCTION DAY_ORD_SF
(
P_IDBASKET IN bb_basket.idbasket%type
)
RETURN VARCHAR2 AS
lv_date_created VARCHAR2(240);
BEGIN
SELECT to_char(dtcreated,'DAY') DAY_CREATED
INTO lv_date_created
FROM BB_BASKET
WHERE IDBASKET = P_IDBASKET;
RETURN lv_date_created;
END DAY_ORD_SF;
/
Or
CREATE OR REPLACE FUNCTION DAY_ORD_SF
(
P_DATE_CREATED IN bb_basket.dtcreated%type
)
RETURN VARCHAR2 AS
BEGIN
RETURN to_char(P_DATE_CREATED,'DAY');
END DAY_ORD_SF;
/