SQL generated columns automate the storage of computed data within a database table. This guide provides an overview and examples to help you understand and implement this feature effectively.
Examples of SQL Generated Columns
Generated columns are created using CREATE TABLE or ALTER TABLE statements. For instance, in MySQL:
ALTER TABLE users
ADD COLUMN fullName VARCHAR(255) AS (CONCAT(name, " ", surname)) STORED;
This command creates a stored generated column combining name and surname.
A virtual column example, which doesn’t occupy storage space, is shown below:
ALTER TABLE users
ADD fullNamePoints VARCHAR(255) AS (CONCAT(fullName, " (", points, ")")) VIRTUAL;
FAQs About Generated Columns
What databases support generated columns?
Generated columns are supported by MySQL, MariaDB, PostgreSQL, SQL Server, and Oracle.
What is the difference between a trigger and a generated column?
Triggers are event-driven scripts affecting multiple tables, while generated columns store automatically computed data in one table.
What are the types of columns generated in SQL?
SQL supports stored (precomputed) and virtual (computed on-the-fly) generated columns.
What is the difference between a generated column and a regular column?
Generated columns are auto-calculated and immutable, whereas regular columns can be manually updated.
Conclusion
SQL generated columns simplify data management by automating calculations. For a comprehensive guide and advanced examples, visit The Ultimate Guide to Generated Columns.