Book Image

MariaDb Essentials

By : Kenler
Book Image

MariaDb Essentials

By: Kenler

Overview of this book

This book will take you through all the nitty-gritty parts of MariaDB, right from the creation of your database all the way to using MariaDB’s advanced features. At the very beginning, we show you the basics, that is, how to install MariaDB. Then, we walk you through the databases and tables of MariaDB, and introduce SQL in MariaDB. You will learn about all the features that have been added in MariaDB but are absent in MySQL. Moving on, you’ll learn to import and export data, views, virtual columns, and dynamic columns in MariaDB. Then, you’ll get to grips with full-text searches and queries in MariaDb. You’ll also be familiarized with the CONNECT storage engine. At the end of the book, you’ll be introduced to the community of MariaDB.
Table of Contents (10 chapters)
9
Index

Virtual and persistent columns

We described a view on a virtual table, meaning that its contents are the results of a query. The idea behind virtual columns is very similar: they are columns based on SQL expressions.

A virtual column overview

The terminology is a bit confusing here. In fact, all automatically calculated columns are called virtual columns in MariaDB KnowledgeBase. However, there are two types of virtual columns: VIRTUAL columns and PERSISTENT columns.

  • A VIRTUAL column is calculated on-the-fly when it is referenced in a statement—for example, when a SELECT clause extracts its value. This is the default type.
  • A PERSISTENT column is written in the table and its value can be read when needed, as happens with regular columns.

Calculating each value on-the-fly is additional work for the CPU, but saves space on the disk. Only PERSISTENT columns can be indexed or used in a foreign key.

In both cases, the calculated values cannot be directly inserted or modified. MariaDB automatically...