Maximize the Potential of MySQL with Generated Columns

Database management is a cornerstone in the development of any modern application, and MySQL stands out as one of the most popular and robust relational database management systems used in the industry. One of the less explored but incredibly powerful aspects of MySQL is generated columns. This article delves into how you can use generated columns to optimize and simplify operations on your databases, thus boosting the performance of your applications.

What are generated columns?

Generated columns, also known as virtual or computed columns, are columns in a MySQL table that do not physically store data. Instead, they calculate their values from expressions or other columns within the same table each time they are accessed. These expressions can include math operations, string functions, dates, and other columns. The definition of a generated column is stored in the MySQL data dictionary and the value is recalculated whenever necessary, always ensuring the accuracy and currency of the data without manual maintenance.

Types of Generated Columns

MySQL offers two types of generated columns:

• Persistent: The values are physically stored in the database, like any other column. This increases the storage size but optimizes the read speed, since the value does not need to be recalculated on each query.

• Virtual: They are not physically stored and their value is recalculated each time they are accessed. Ideal for values that are rarely consulted or when storage is a concern.

Benefits of Using Generated Columns

Implementing generated columns offers multiple benefits, including:

• Performance Optimization: Reduces the need to calculate values when performing queries, which is especially useful in large, complex tables.

• Data Integrity- Maintains data accuracy as values are automatically calculated based on defined expressions.

• Simplicity in Queries: Simplifies SQL queries by eliminating the need to include complex and repetitive calculations in each query.

Practical Example of Generated Columns

Imagine that you have a table products what includes price y amount of products, and you want to keep a record of the total_value of each product (calculated as price * quantity). Instead of manually updating total_value Everytime that price o amount changes, you could define a generated column like this:

CREATE TABLE products ( id INT AUTO_INCREMENT PRIMARY KEY, name VARCHAR(50), price DECIMAL(10, 2), quantity INT, total_value DECIMAL(10, 2) AS (price * quantity) STORED );

In this example, total_value is a generated column of persisted type, which means that its value is calculated and stored every time the values of price o amount are modified.

How to Implement Generated Columns in MySQL

Implementing generated columns in MySQL is a straightforward process. Here I show you how you can add a generated column to an existing table:

Generated Column Addition Example

Let's say you want to add a column that stores the price with VAT to an existing table. You could do it like this:

ALTER TABLE products ADD COLUMN price_with_vat DECIMAL(10, 2) AS (price * 1.16) VIRTUAL;

In this case, price_with_vat is a virtual generated column that is recalculated each time it is accessed, basing its value on the current price plus a 16% VAT.

Best Practices and Considerations

Although the generated columns are extremely useful, it is crucial to use them wisely:

1. Evaluate Column Type: Decide between virtual and persisted based on access frequency and the importance of read performance.
2. Limit Use on Large Tables: For large tables with many writes, excessive use of generated columns can degrade performance.
3. Monitor Performance- Constantly analyzes query performance and adjusts the implementation of generated columns as necessary.

Conclusion

Generated columns are a powerful feature of MySQL that, when used correctly, can significantly simplify database design and improve application performance. By automating calculations and ensuring data integrity, they facilitate the maintenance and scalability of database applications.

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