This article shows you how to use AFTER INSERT TRIGGER, it will fire after the insert operation is executed.

1. After INSERT Trigger

In this example, if a new user is created in user_details, but fields like passport_no or driving_license_no is missing, a new record will be inserted into user_reminders via ‘after insert’ trigger on user_details

1.1 Create tables and trigger.

CREATE TABLE USER_DETAILS
	USER_ID number(10) primary key,
	USER_NAME varchar2(15),
	EMAIL varchar2(20),
	PHONE number(12),
	PASSPORT_NO varchar2(10),
	DRIVING_LICENSE_NO varchar2(10)
);

CREATE TABLE USER_REMINDERS
	USER_ID number(10),
	REMINDER_TEXT varchar2(200),
	REMINDER_DATE date,
	STATUS varchar2(10)
);

CREATE OR REPLACE TRIGGER trg_after_insert_user
AFTER INSERT
  on USER_DETAILS
  FOR EACH ROW 
DECLARE
counter number(2);
reminder_text varchar2(200);
BEGIN
counter := 0;
reminder_text := '';
  IF(:NEW.PASSPORT_NO = '' OR :NEW.PASSPORT_NO is null) THEN
    reminder_text := 'Please insert your passport details into system. ';
    counter := counter+1;
  END IF;  
  IF(:NEW.DRIVING_LICENSE_NO = '' OR :NEW.DRIVING_LICENSE_NO is null) THEN
    reminder_text := reminder_text || 'Please insert your Driving license details into system.';
    counter := counter+1;
  END IF;  
  -- If passport_no and/or driving_license_no is missing 
  -- then counter will be >0 and below code will insert into user_reminders table.
  IF(counter>0) THEN
    INSERT INTO USER_REMINDERS VALUES (:NEW.USER_ID,reminder_text,sysdate+3,'PENDING');
  END IF;
END;

1.2 Insert data to test the trigger.

-- fire after insert trigger, no action.
INSERT INTO USER_DETAILS VALUES (1,'USERNM1','abcdxyz@abc.com',9999999999,'PASSNUM123','DRIVLIC999');
-- fire after insert trigger, password is null, insert new record into USER_REMINDERS  
INSERT INTO USER_DETAILS VALUES (2,'USERNM22','xyzabcd@abc.com',1111111111,null,'LICNC12345');
-- fire after insert trigger, password and driving no are null, insert new record into USER_REMINDERS 
INSERT INTO USER_DETAILS VALUES (3,'USERNM33','xyztttt@abc.com',3333333333,null,null);
-- fire after insert trigger, driving no is null, insert new record into USER_REMINDERS 
INSERT INTO USER_DETAILS VALUES (4,'USERNM44','ghijkl@abc.com',4444444444,'ONLYPASS11',null);

1.3 Display the data.

select * from USER_DETAILS;

select * from USER_REMINDERS;

References

1. Creating a DML Trigger: Examples
2. PL/SQL Triggers :- Oracle official docs
3. Oracle PL/SQL – Before INSERT Trigger example