Generated columns in SQL automatically compute and store data, simplifying database operations. This article offers a brief overview and practical examples to demonstrate their use.
Examples of SQL Generated Columns
In SQL, generated columns are defined via CREATE TABLE or ALTER TABLE. Here’s an example using MySQL:
ALTER TABLE users
ADD COLUMN fullName VARCHAR(255) AS (CONCAT(name, " ", surname)) STORED;
This adds a stored column fullName that concatenates name and surname.
For a virtual column, which doesn’t use storage space:
ALTER TABLE users
ADD fullNamePoints VARCHAR(255) AS (CONCAT(fullName, " (", points, ")")) VIRTUAL;
FAQs About Generated Columns
What databases support generated columns?
Databases like MySQL, MariaDB, PostgreSQL, SQL Server, and Oracle support generated columns.
What is the difference between a trigger and a generated column?
Triggers execute scripts on events affecting multiple tables, whereas generated columns store auto-calculated data in one table.
What are the types of columns generated in SQL?
SQL has 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, unlike regular columns which are manually updated.
Conclusion
SQL generated columns automate data calculations, enhancing database efficiency. For an in-depth guide and more examples, check out The Ultimate Guide to Generated Columns.