Cannot insert NULL into, ERROR during execution of trigger - oracle

Question

I have created a Trigger on table Customers so that every time a record is deleted from table customers this same record is inserted in table Customer_Archives with the current date as Deletion_Date.
I am have to insert a new customer into table Customers and then delete it. The record must be inserted correctly into table Customers_Archive.
Here's script I have so far:
CREATE TABLE Customer_Archives
(
customer_id NUMBER NOT NULL,
customer_first_name VARCHAR2(50),
customer_last_name VARCHAR2(50) NOT NULL,
customer_address VARCHAR2(255) NOT NULL,
customer_city VARCHAR2(50) NOT NULL,
customer_state CHAR(2) NOT NULL,
customer_zip VARCHAR2(20) NOT NULL,
customer_phone VARCHAR2(30) NOT NULL,
customer_fax VARCHAR2(30),
deletion_date DATE,
CONSTRAINT customer_archives_pk
PRIMARY KEY (customer_id)
);
CREATE OR REPLACE TRIGGER Customers_before_insert
BEFORE DELETE ON Customers
FOR EACH ROW
DECLARE
ar_row Customers%rowtype;
BEGIN
INSERT INTO Customer_Archives
VALUES(ar_row.Customer_id,
ar_row.Customer_First_Name,
ar_row.Customer_Last_Name,
ar_row.Customer_Address,
ar_row.Customer_City,
ar_row.Customer_State,
ar_row.Customer_Zip,
ar_row.Customer_Phone,
ar_row.Customer_Fax,
sysdate());
dbms_output.put_line('New row is added to Customers_Archive
Table with Customer_ID:' ||ar_row.Customer_id ||'on date:' || sysdate());
END;
/
SELECT trigger_name, status FROM user_triggers;
INSERT INTO CUSTOMERS
(customer_id, customer_first_name, customer_last_name, customer_address,
customer_city, customer_state, customer_zip, customer_phone, customer_fax)
VALUES (27,'Sofia','Chen','8888 Cowden St.','Philadelphia','PA',
'19149',7654321234',NULL);
DELETE FROM CUSTOMERS
WHERE customer_id = 27;
When I try to delete the customer that I just inserted I get an error:
Error starting at line : 47 in command -
DELETE FROM CUSTOMERS
WHERE customer_id = 27
Error report -
ORA-01400: cannot insert NULL into ("TUG81959"."CUSTOMER_ARCHIVES"."CUSTOMER_ID")
ORA-06512: at "TUG81959.CUSTOMERS_BEFORE_INSERT", line 4
ORA-04088: error during execution of trigger 'TUG81959.CUSTOMERS_BEFORE_INSERT'

Answer 1

In your DELETE trigger you should be using the :OLD values when creating your archive record:
CREATE OR REPLACE TRIGGER CUSTOMERS_BEFORE_INSERT
BEFORE DELETE ON CUSTOMERS
FOR EACH ROW
BEGIN
INSERT INTO CUSTOMER_ARCHIVES
(CUSTOMER_ID,
CUSTOMER_FIRST_NAME,
CUSTOMER_LAST_NAME,
CUSTOMER_ADDRESS,
CUSTOMER_CITY,
CUSTOMER_STATE,
CUSTOMER_ZIP,
CUSTOMER_PHONE,
CUSTOMER_FAX,
DELETION_DATE)
VALUES
(:OLD.CUSTOMER_ID,
:OLD.CUSTOMER_FIRST_NAME,
:OLD.CUSTOMER_LAST_NAME,
:OLD.CUSTOMER_ADDRESS,
:OLD.CUSTOMER_CITY,
:OLD.CUSTOMER_STATE,
:OLD.CUSTOMER_ZIP,
:OLD.CUSTOMER_PHONE,
:OLD.CUSTOMER_FAX,
SYSDATE());
DBMS_OUTPUT.PUT_LINE('New row is added to Customers_Archive
Table with Customer_ID:' ||:OLD.Customer_id ||'on date:' || SYSDATE());
END;
In your original trigger you'd declared a row variable named ar_row but hadn't assigned anything to any of the fields - therefore they were all NULL. When a BEFORE trigger is invoked during a DELETE, the :OLD values have the values prior to the deletion, and the :NEW values are all NULL.
Best of luck.