Understanding SQL Generated Columns for Efficient Data Management

SQL generated columns are an advanced feature that helps in storing automatically calculated data within a table. They streamline database operations by reducing the need for repetitive queries. This article provides a concise overview and examples of SQL generated columns.

Examples of SQL Generated Columns

SQL generated columns are defined using the CREATE TABLE or ALTER TABLE commands. Here’s a quick example using MySQL:

ALTER TABLE users
ADD COLUMN fullName VARCHAR(255) AS (CONCAT(name, " ", surname)) STORED;

In this case, fullName is a generated column that combines the name and surname columns.

For virtual columns, which do not take up storage space, the definition looks like this:

ALTER TABLE users
ADD fullNamePoints VARCHAR(255) AS (CONCAT(fullName, " (", points, ")")) VIRTUAL;

FAQ

What databases support generated columns?

Many relational 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 SQL scripts based on events, affecting multiple tables, while generated columns store auto-calculated data within a single table.

What are the types of columns generated in SQL?

There are two types: stored (precomputed and stored) and virtual (calculated on-the-fly).

What is the difference between a generated column and a regular column?

Generated columns have values calculated automatically and can’t be manually changed, unlike regular columns.

Conclusion

SQL generated columns enhance database efficiency by automating data calculations. For more detailed insights and examples please read The Ultimate Guide to Generated Columns.