triggers and events

Author: ptyadana

Diff for: Complete SQL Mastery - Mosh/Triggers and Events.sql

@@ -0,0 +1,154 @@
+/************************************************/
+/*       Triggers                               */
+/************************************************/
+
+SELECT * FROM mosh_sql_invoicing.invoices;
+SELECT * FROM mosh_sql_invoicing.payments;
+
+/* update total of invoice table, if there is payment added to the payment table */
+USE mosh_sql_invoicing;
+
+DELIMITER $$
+CREATE TRIGGER payments_after_insert
+	AFTER INSERT ON payments
+    FOR EACH ROW
+BEGIN
+	UPDATE invoices
+    SET payment_total = payment_total + NEW.amount
+    WHERE invoice_id = NEW.invoice_id;
+END $$
+DELIMITER ;
+
+/*testing*/
+INSERT INTO payments
+VALUES(DEFAULT,5,3,'2020-04-05',100,1);
+
+
+/* trigger that gets fired when we delete the payment */
+DROP TRIGGER IF EXISTS payments_after_delete;
+
+DELIMITER $$
+CREATE TRIGGER payments_after_delete
+	AFTER DELETE ON payments
+    FOR EACH ROW
+BEGIN
+	UPDATE invoices
+    SET payment_total = payment_total - OLD.amount
+    WHERE invoice_id = OLD.invoice_id;
+END $$
+DELIMITER ;
+
+/*testing*/
+DELETE FROM payments
+WHERE payment_id = 9;
+
+/************************************************/
+/*       View Triggers                          */
+/************************************************/
+SHOW TRIGGERS;
+
+SHOW TRIGGERS LIKE '%payments%';
+
+
+/************************************************/
+/*       Drop Triggers                          */
+/************************************************/
+
+DROP TRIGGER IF EXISTS payments_after_delete;
+
+
+/************************************************/
+/*       Using Triggers for Auditing            */
+/************************************************/
+
+USE mosh_sql_invocing;
+
+CREATE TABLE payments_audit(
+	client_id INT NOT NULL,
+    date DATE NOT NULL,
+    amount DECIMAL(9,2) NOT NULL,
+    action_type VARCHAR(50) NOT NULL,
+    action_date DATETIME NOT NULL
+);
+
+/*trigger for auditing records for insert */
+DROP TRIGGER IF EXISTS payments_after_insert;
+
+DELIMITER $$
+CREATE TRIGGER payments_after_insert
+	AFTER INSERT ON payments
+    FOR EACH ROW
+BEGIN
+	UPDATE invoices
+    SET payment_total = payment_total + NEW.amount
+    WHERE invoice_id = NEW.invoice_id;
+    
+    INSERT INTO payments_audit
+    VALUES(NEW.client_id, NEW.date, NEW.amount, 'INSERT', NOW());
+END $$
+DELIMITER ;
+
+
+/*trigger for auditing records for delete */
+DROP TRIGGER IF EXISTS payments_after_delete;
+
+DELIMITER $$
+CREATE TRIGGER payments_after_delete
+	AFTER DELETE ON payments
+    FOR EACH ROW
+BEGIN
+	UPDATE invoices
+    SET payment_total = payment_total - OLD.amount
+    WHERE invoice_id = OLD.invoice_id;
+    
+    INSERT INTO payments_audit
+    VALUES(OLD.client_id, OLD.date, OLD.amount, 'DELETE', NOW());
+END $$
+DELIMITER ;
+
+
+/*testing*/
+SELECT * FROM payments_audit;
+
+INSERT INTO payments
+VALUES(DEFAULT,5,3,'2020-04-05',100,1);
+
+DELETE FROM payments
+WHERE payment_id = 10;
+
+
+/***************************************************/
+/*      Events                                     */
+/* Tasks that get executed according to a scheduel */
+/***************************************************/
+
+SHOW VARIABLES LIKE 'event%';
+
+-- usually it is ON, but some organiazion it might be turned off to save resources.
+SET GLOBAL event_scheduler = ON;
+
+/* events that delete all the audit recrods which are 1 year old from today */
+DELIMITER $$
+CREATE EVENT yearly_delete_stale_audit_rows
+ON SCHEDULE
+	EVERY 1 YEAR STARTS '2020-01-01' ENDS '2030-12-31'
+DO BEGIN
+	DELETE FROM payments_audit
+    WHERE action_date < NOW() - INTERVAL 1 YEAR;
+END $$
+DELIMITER ;
+
+
+/***************************************************/
+/* View / Alter / Drop Events  / Disable / Enable  */
+/***************************************************/
+
+SHOW EVENTS;
+
+SHOW EVENTS like 'montly%';
+
+DROP EVENT IF EXISTS yearly_delete_stale_audit_rows;
+
+ALTER EVENT yearly_delete_stale_audit_rows DISABLE;
+
+ALTER EVENT yearly_delete_stale_audit_rows ENABLE;