add: triggers

sql/full_course/db_table/trigger.sql

@@ -0,0 +1,79 @@
+-- Trigger = When an event happends, do something
+--           ex. (INSERT, UPDATE, DELETE)
+--           checks data, handle errors, auditing tables
+
+SELECT * FROM employees;
+
+ALTER TABLE employees
+ADD COLUMN salary DECIMAL(10, 2) AFTER hourly_pay;
+
+UPDATE employees
+SET salary = hourly_pay * 2080;
+
+CREATE TRIGGER before_hourly_pay_update
+BEFORE UPDATE ON employees
+FOR EACH ROW
+SET NEW.salary = (NEW.hourly_pay * 2080);
+
+CREATE TRIGGER before_hourly_pay_insert
+BEFORE INSERT ON employees
+FOR EACH ROW
+SET NEW.salary = (NEW.hourly_pay * 2080);
+
+SHOW TRIGGERS;
+
+SELECT * FROM employees;
+
+UPDATE employees
+SET hourly_pay = 50
+WHERE employee_id = 1;
+
+INSERT INTO employees
+VALUES(6, "Sheldon", "Plankton", "sheldon@gmail.com", 10, NULL, "janitor", "2025-03-03", 5);
+
+--------------------------
+
+CREATE TABLE wages(
+    wage_id INT PRIMARY KEY AUTO_INCREMENT,
+    wage_name VARCHAR(50),
+    wage_total DECIMAL(10, 2)
+);
+
+SELECT * FROM wages;
+
+INSERT INTO wages (wage_name, wage_total)
+VALUES ("salaries", 0),
+       ("supplies", 0),
+       ("taxes", 0);
+
+UPDATE wages
+SET wage_total = (SELECT SUM(salary) FROM employees)
+WHERE wage_name = "salaries";
+
+CREATE TRIGGER after_salary_upate
+AFTER DELETE ON employees
+FOR EACH ROW
+UPDATE wages
+SET wage_total = wage_total - OLD.salary
+WHERE wage_name = "salaries";
+
+CREATE TRIGGER after_salary_insert
+AFTER INSERT ON employees
+FOR EACH ROW
+UPDATE wages
+SET wage_total = wage_total + NEW.salary
+WHERE wage_name = "salaries";
+
+CREATE TRIGGER after_salary_update
+AFTER UPDATE ON employees
+FOR EACH ROW
+UPDATE wages
+SET wage_total = wage_total + (NEW.salary - OLD.salary)
+WHERE wage_name = "salaries";
+
+SHOW TRIGGERS;
+
+SELECT * FROM wages;
+
+DELETE FROM employees
+WHERE employee_id = 6;