Values of a generated (virtual) column are computed from an expression included in the column definition.
Hey there fellow database enthusiasts! Have you ever wished you could calculate values when storing data to your MySQL tables? Well, look no further because today we’re diving into the exciting world of MySQL virtual columns!
Benefits & usage:
- Dynamic calculated fields: Creating calculated fields based on other columns’ values. For example, calculating a product’s total price by multiplying its quantity and unit price.
- Data normalization: Keeping data normalized in the database by storing derived values as virtual columns.
- Performance optimization: Improving query performance by eliminating the need for additional, redundant data storage or complex JOIN operations.
- Improving data organization: Adding derived columns to a table that help in organizing and categorizing the data in a more meaningful way.
- Dynamic grouping: Grouping data based on virtual columns, without the need to physically store the grouping column.
Consider a table named “products” that stores information about products in an e-commerce store. This table has the following columns:
- product_id (primary key)
We can create a virtual column named “total_price” that calculates the total price for each product by multiplying its quantity and unit price, as follows:
ALTER TABLE products ADD COLUMN total_price AS (quantity * unit_price);
When selecting data from the “products” table, we will have access to the calculated “total_price” field without having to store it physically in the table. This can help improve query performance, as we don’t have to repeat the calculation every time we access the data.
Or let’s consider a table named “employees” that stores information about employees in a company. This table has the following columns:
- employee_id (primary key)
We can create a virtual column named “years_employed” that calculates the number of years an employee has been with the company, as follows:
ALTER TABLE employees ADD COLUMN years_employed AS (YEAR(CURDATE()) - YEAR(hire_date));
Now that we’re getting warmed up, how about implementing virtual columns in the pursuit of fuzzy searching?
Consider a table named “customers” that stores information about customers in a retail store. This table has the following columns:
- customer_id (primary key)
We can create virtual columns that help implement a fuzzy search based on the customer’s name, as follows:
ALTER TABLE customers ADD COLUMN search_name AS (REGEXP_REPLACE(CONCAT(first_name, ' ', last_name), '[^a-zA-Z0-9]+', ''));
Now, we can use the virtual column “search_name” to perform a fuzzy search based on the customer’s full name, while also removing any special characters. For example, if we search the name “Tim O’reilly or Tim Oreilly”, we’ll get the appropriate result (by disregarding the apostrophe). Now we’re simplifying our search logic by avoiding having to write complex string manipulations or multiple LIKE clauses in our queries.
Something to consider:
While virtual columns can be a huge benefit, there are some considerations:
- Performance: Can impact query performance, especially for complex expressions or for large tables. Queries that involve virtual columns may require additional processing to evaluate the expression for each row, which can slow down the query.
- Storage: They do not physically store data, they only store the expression used to calculate the value. This means that the expression must be re-evaluated every time the virtual column is used in a query.
- Limited indexes: They can be indexed, but the type of index that can be used is limited. For example, virtual columns can be indexed with a B-Tree index, but not with a full-text index.
- Maintenance: Must be updated whenever the underlying data changes, which can require additional maintenance. If the expression used to calculate the virtual column is complex, it can be more difficult to maintain.
- Compatibility: Not supported by all database systems, and their implementation may differ between systems. This can impact portability and compatibility with other databases.
Considering these limitations, virtual columns should be used with caution and only when they provide a significant benefit in terms of functionality or performance. It may be necessary to periodically evaluate the impact of virtual columns on the database and make changes as needed to ensure optimal performance and stability.