Add new column with Boolean in PL/SQL - sql

Question

I'm learning PL/SQL right now and I have a doubt.
I have created the following table called tbProducts:
CREATE TABLE tbProducts (
nIDProduct NUMBER(2) NOT NULL,
vDescription VARCHAR2(20 CHAR),
nQuantity NUMBER(3),
nPrice NUMBER(6,2),
dLastDate DATE)
And I have inserted some values so the table is like this:
nIDProduct | vDescription | nQuantity | nPrice | dLastDate
1 | 'Hammer' | 50 | 3.25 | 13-MAY-2021
2 | 'Nails' | 100 | 0.75 | 28-AUG-2021
3 | 'Screws' | 250 | 0.16 | 21-JUL-2021
Now what I'm looking for is a boolean variable that can be called bUpdate that returns FALSE if today's date (26-AUG-2021) is greater than dLastDate and returns TRUE if it's less or equal so the table would look like this:
nIDProduct | vDescription | nQuantity | nPrice | dLastDate | bUpdate
1 | 'Hammer' | 50 | 3.25 | 13-MAY-2021 | FALSE
2 | 'Nails' | 100 | 0.75 | 28-AUG-2021 | TRUE
3 | 'Screws' | 250 | 0.16 | 21-JUL-2021 | FALSE
I am trying doing the following:
DECLARE
bUpdate BOOLEAN;
BEGIN
SELECT t.*, bUpdate(
IF SYSDATE > dLastDate THEN
bUpdate := FALSE;
ELSE
bUpdate := TRUE;
END IF
FROM tbProducts t
;
END;
I get an error saying that a FROM was expected after the SELECT statement.
Since I'm still learning I don't know what it's wrong in this statement, could someone help me? Is there a way to do it with a CURSOR too?
Thank you all!

Answer 1

What you try wouldn't work. If you want an additional column, you need to add the column to the table with an ALTER TABLE command - but in this case you're adding a non-deterministic expression and that cannot be added as a virtual column.
The easiest way to achieve what you want is to create a view on top of the table with the case statement as illustrated below:
CREATE TABLE tbproducts (
nidproduct NUMBER(2) NOT NULL,
vdescription VARCHAR2(20 CHAR),
nquantity NUMBER(3),
nprice NUMBER(6,2),
dlastdate DATE);
INSERT INTO tbproducts (nidproduct,vdescription,nquantity,nprice,dlastdate) VALUES (1,'Hammer', 50,3.25,TO_DATE('13-MAY-2021','DD-MON-YYYY'));
INSERT INTO tbproducts (nidproduct,vdescription,nquantity,nprice,dlastdate) VALUES (2, 'Nails',100,0.75,TO_DATE('28-AUG-2021','DD-MON-YYYY'));
INSERT INTO tbproducts (nidproduct,vdescription,nquantity,nprice,dlastdate) VALUES (3,'Screws',250,0.16,TO_DATE('21-JUL-2021','DD-MON-YYYY'));
CREATE VIEW tbproducts_v
AS
SELECT
nidproduct
,vdescription
,nquantity
,nprice
,dlastdate
,CASE WHEN SYSDATE > dlastdate THEN 'TRUE' ELSE 'FALSE' END as status
FROM tbproducts;
select * from tbproducts_v;
NIDPRODUCT VDESCRIPTION NQUANTITY NPRICE DLASTDATE STATU
---------- -------------------- ---------- ---------- ----------- -----
1 Hammer 50 3.25 13-MAY-2021 TRUE
2 Nails 100 .75 28-AUG-2021 FALSE
3 Screws 250 .16 21-JUL-2021 TRUE
If you insist on adding a new column then this is what you'd do.
ALTER TABLE tbproducts ADD status VARCHAR2(100);
UPDATE tbproducts t
SET (t.status) =
(SELECT
CASE WHEN SYSDATE > dlastdate THEN 'TRUE' ELSE 'FALSE' END
FROM tbproducts st
WHERE st.nidproduct = t.nidproduct);
if you just want to display the true/false in the console with a pl/sql block then this is an option (using implicit cursor for loop):
set serveroutput on size 999999
clear screen
DECLARE
BEGIN
FOR r IN (SELECT * FROM tbproducts) LOOP
dbms_output.put_line('Product '||r.vdescription ||', status: '||CASE WHEN SYSDATE > r.dlastdate THEN 'TRUE' ELSE 'FALSE' END);
IF r.dlastdate < SYSDATE THEN
dbms_output.put_line('Product '||r.vdescription ||' is expired !');
END IF;
END LOOP;
END;
/
note 1 : pl/sql has a boolean datatype, but sql does NOT have one. So in your table you'll need to store a string (1/0, T/F, Y/N, TRUE/FALSE).
note 2 : it's not a good practice to use camelcase in table names or column names. If you're creating them without quotes the names are case insensitive anyway.