**Course Title:** SQLite Mastery: Lightweight Database Management **Section Title:** Views, Triggers, and Advanced Features **Topic:** Write SQL scripts to create views and triggers in an SQLite database.(Lab topic) **Introduction** In the previous topics, we have explored the fundamental concepts of SQLite and its various features. In this lab topic, we will delve into creating views and triggers in an SQLite database using SQL scripts. Views and triggers are essential in database design, as they help to simplify complex queries, ensure data integrity, and improve database performance. **Understanding Views and Triggers** **Views:** A view is a virtual table that is derived from one or more existing tables in the database. It is a stored query that can be treated like a table. Views are useful when you need to: * Simplify complex queries * Restrict data access to certain users * Provide a layer of abstraction between the physical table and the user **Triggers:** A trigger is a set of actions that are executed in response to a specific event on a table, such as INSERT, UPDATE, or DELETE. Triggers can be used to: * Enforce data integrity constraints * Automate actions on data changes * Auditing and logging **Writing SQL scripts to create views** To create a view in SQLite, you use the `CREATE VIEW` statement. The syntax is as follows: ```sql CREATE VIEW [schema_name].[view_name] AS SELECT column1, column2, ... FROM table_name [WHERE condition] [GROUP BY column1, column2, ...] [HAVING condition]; ``` **Example 1: Creating a simple view** Suppose we have a table called `employees` with columns `name`, `age`, and `salary`. We want to create a view that shows only the employees whose salary is greater than $50,000. ```sql CREATE VIEW high_salary_employees AS SELECT name, age, salary FROM employees WHERE salary > 50000; ``` **Example 2: Creating a view with multiple tables** Suppose we have two tables, `customers` and `orders`, and we want to create a view that shows the customer name and order date for each order. ```sql CREATE VIEW customer_orders AS SELECT c.name, o.order_date FROM customers c JOIN orders o ON c.customer_id = o.customer_id; ``` **Writing SQL scripts to create triggers** To create a trigger in SQLite, you use the `CREATE TRIGGER` statement. The syntax is as follows: ```sql CREATE TRIGGER [schema_name].[trigger_name] BEFORE|AFTER|INSTEAD OF {INSERT|UPDATE|DELETE} ON [schema_name].[table_name] FOR EACH {ROW|STATEMENT} EXECUTE PROCEDURE [schema_name].[function_name]; ``` **Example 1: Creating a trigger to enforce data integrity** Suppose we have a table called `employees` with columns `name`, `age`, and `salary`. We want to create a trigger that ensures the salary is greater than $50,000 for each employee. ```sql CREATE TRIGGER check_salary BEFORE INSERT OR UPDATE OF salary ON employees FOR EACH ROW BEGIN IF NEW.salary <= 50000 THEN RAISE(ABORT, 'Salary must be greater than 50000'); END IF; END; ``` **Example 2: Creating a trigger to automate actions on data changes** Suppose we have a table called `orders` with columns `order_id`, `customer_id`, and `order_date`. We want to create a trigger that inserts a new record into the `order_history` table when an order is updated. ```sql CREATE TRIGGER update_order_history AFTER UPDATE OF order_date ON orders FOR EACH ROW BEGIN INSERT INTO order_history (order_id, customer_id, order_date) VALUES (OLD.order_id, OLD.customer_id, OLD.order_date); END; ``` **Conclusion** In this lab topic, we have covered the basics of creating views and triggers in SQLite using SQL scripts. We have explored the syntax and examples of creating views and triggers, and we have seen how they can be used to simplify complex queries, ensure data integrity, and automate actions on data changes. Remember to practice creating views and triggers on your own to become more proficient in using these powerful features. **What to Do Next** Now that you have learned how to create views and triggers in SQLite, you can try to: * Create a view that shows the top-selling products for each category. * Create a trigger that ensures the customer name is not empty for each order. * Create a trigger that updates the order status when the payment is received. **External Resources** * SQLite Documentation: [https://sqlite.org/docs.html](https://sqlite.org/docs.html) * W3Schools SQLite Tutorial: [https://www.w3schools.com/sql/sql_lite.asp](https://www.w3schools.com/sql/sql_lite.asp) **Do You Have Questions or Need Help?** Leave a comment below if you have any questions or need help with creating views and triggers in SQLite.