MySQL View

A MySQL view is a virtual table that is derived from one or more existing tables in a database. It is a saved SELECT statement that can be used like a table in queries, but it does not actually store any data itself. Instead, it pulls data from the underlying tables based on the criteria specified in the view’s SELECT statement.

Views are used to simplify queries and make them more readable and efficient. They can also be used to restrict access to sensitive data by allowing users to query only a subset of the data in a table. Views can be created, modified, and deleted using SQL commands or visual tools provided by MySQL management software.

In addition to simplifying queries and improving security, views can also be used to aggregate data from multiple tables, provide calculated values, and perform other transformations on data before it is presented to the user.

There are several benefits of using MySQL views:

1. Simplify complex queries: Views allow you to create complex queries that can be saved and reused, making it easier to write and maintain SQL code.
2. Improved performance: Views can improve performance by precomputing complex calculations or aggregations and caching the results.
3. Enhanced security: Views can be used to restrict access to sensitive data by allowing users to query only a subset of the data in a table.
4. Data abstraction: Views provide a layer of abstraction that allows you to work with data at a higher level of abstraction than tables, making it easier to work with data in a more meaningful way.
5. Data consistency: Views can be used to enforce data consistency by restricting data modifications to a specific subset of the data.
6. Simpler application development: Views can simplify application development by encapsulating complex business logic and calculations, making it easier to change the underlying data model without affecting the application code.

Overall, MySQL views are a powerful tool that can simplify SQL queries, improve performance, and enhance security, making it easier to work with data in a more meaningful way.

Let’s say you have a database with two tables: orders and customers. The orders table contains information about customer orders, including the customer ID, order date, and order total. The customers table contains information about each customer, including their name, email address, and phone number.

If you want to retrieve a list of all orders with the customer name and email address included, you might use a JOIN statement like this:

SELECT orders.order_id, orders.order_date, orders.order_total, customers.customer_name, customers.customer_email 
FROM orders
JOIN customers ON orders.customer_id = customers.customer_id;

However, this query can be complex and difficult to read. To simplify it, you can create a view that encapsulates the JOIN statement:

CREATE VIEW order_details AS
SELECT orders.order_id, orders.order_date, orders.order_total, customers.customer_name, customers.customer_email 
FROM orders
JOIN customers ON orders.customer_id = customers.customer_id;

Now, you can retrieve the same information with a simpler query:

SELECT * FROM order_details;

This query retrieves the same information as the previous example, but the underlying complexity of the JOIN statement is abstracted away into the view definition. This makes it easier to read and maintain your code.

Add Trigger with daily update MySQL View

Assuming you have a view called order_details, and you want to update it every day at midnight, you can create an event that updates the view and schedules it to run daily.

First, you need to enable the event scheduler if it is not already enabled:

SET GLOBAL event_scheduler = ON;

Then, you can create an event that updates the view:

CREATE EVENT daily_update
ON SCHEDULE EVERY 1 DAY
STARTS '2023-03-11 00:00:00'
DO
CREATE OR REPLACE VIEW order_details AS
SELECT orders.order_id, orders.order_date, orders.order_total, customers.customer_name, customers.customer_email
FROM orders
JOIN customers ON orders.customer_id = customers.customer_id;

n this example, the daily_update event is scheduled to run every day at midnight, starting on March 11, 2023. When the event runs, it executes a CREATE OR REPLACE VIEW statement to update the order_details view with the latest data.

Note that you can modify the event schedule to suit your needs, such as running the event at a different time or frequency. Also, make sure to test your trigger thoroughly to ensure that it works as expected.