The Theory

Generated Columns is a feature released on MySQL 5.7. They can be used during CREATE TABLE or ALTER TABLE statements. It is a way of storing data without actually sending it through the INSERT or UPDATE clauses in SQL. The database resolves what the data will be.

There are two types of Generated Columns: Virtual and Stored. They work with:

• mathematical expressions (product_price * quantity)
• built-in functions (RIGHT(), CONCAT(), FROM_UNIXTIME(), JSON_EXTRACT())
• literals (“2”, “new”, 0)

Besides that, they can be indexed but they don’t allow …

In MySQL 5.7.6, we added a new feature called Generated Columns. In the initial work all Generated Columns were materialized, even virtual ones. This not only resulted in unnecessary disk space being used and disk I/O being done, but it also meant that any table alteration required that the full table be rebuilt. In the new MySQL 5.7.7 JSON Lab release, we have resolved all of these issues by implementing new features that not only allow users to create non-materialized virtual …