P8 - Trigger

Problem Statement: Write a Row Level Before and After Trigger on Library table. The System should keep track of the records that are being updated or deleted. The old value of updated or deleted records should be added in Library_Audit table.

Creating tables

CREATE TABLE Library(
    id NUMBER(12),
    title VARCHAR(255),
    dateofissue DATE,
    author VARCHAR(255)
);

CREATE TABLE Library_Audit(
    id NUMBER(12),
    title VARCHAR(255),
    dateofaction DATE,
    author VARCHAR(255),
    status VARCHAR(255)
);

Inserting values

INSERT INTO Library VALUES (1, 'Berserk', TO_DATE('2024-07-28','YYYY-MM-DD'), 'Prashant');
INSERT INTO Library VALUES (2, 'Dark', TO_DATE('2024-07-15','YYYY-MM-DD'), 'Rajendra');
INSERT INTO Library VALUES (3, 'Hannibal', TO_DATE('2024-07-20','YYYY-MM-DD'), 'Manoj');
INSERT INTO Library VALUES (4, 'AOT', TO_DATE('2024-07-30','YYYY-MM-DD'), 'Rajesh');
INSERT INTO Library VALUES (5, 'GOT', TO_DATE('2024-07-19','YYYY-MM-DD'), 'Anil');

Trigger

CREATE OR REPLACE TRIGGER library_action
AFTER INSERT OR UPDATE OR DELETE
ON Library
FOR EACH ROW
BEGIN
	IF INSERTING THEN
    	INSERT INTO Library_Audit (id, title, dateofaction, author, status) VALUES (:NEW.id, :NEW.title, current_timestamp, :NEW.author, 'Insert');
	ELSIF UPDATING THEN
        INSERT INTO Library_Audit (id, title, dateofaction, author, status) VALUES (:OLD.id, :OLD.title, current_timestamp, :OLD.author, 'Update');
	ELSIF DELETING THEN
        INSERT INTO Library_Audit (id, title, dateofaction, author, status) VALUES (:OLD.id, :OLD.title, current_timestamp, :OLD.author, 'Delete');
	END IF;
END;
/

Testing trigger

Insert operation

INSERT INTO Library VALUES (15, 'CREW', TO_DATE('2024-07-22','YYYY-MM-DD'), 'Ramesh');
INSERT INTO Library VALUES (14, 'Ninteen Eighty Four', TO_DATE('2024-07-01','YYYY-MM-DD'), 'Omkar');

SELECT * FROM Library;
SELECT * FROM Library_Audit;

Update operation

UPDATE Library SET id = 6, title = 'Sherlock', author = 'Deepak' where id = 3;
UPDATE Library SET id = 7, title = 'MR. ROBOT', author = 'Varad' where id = 4;

SELECT * FROM Library;
SELECT * FROM Library_Audit;

Delete operation

DELETE FROM Library WHERE id = 1;
DELETE FROM Library WHERE id = 5;

SELECT * FROM Library;
SELECT * FROM Library_Audit;

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