Operations on databases can be complex. Often, MariaDB has to examine several data to find the rows that we want to read. It may also have to perform complex operations, such as aggregating data or sorting values. Typical operations on data will be described in Chapter 3, Getting Started with SQL. Here we will briefly discuss the data structure used to optimize these operations—that is, indexes. Key is a synonym for index.
Note
Note that different storage engines implement indexes in different ways. The following discussion refers to InnoDB, which is the most commonly used engine. If we use other engines, such as MEMORY or MyISAM, we may need to check the MariaDB KnowledgeBase to learn how these engines handle indexes.
To explain what an index is, we are going to use a typical example: a book's index. Imagine we have to find a topic, or some specific information, in a big book that we have never read before, and which does not have an index. We would need a lot of time! But fortunately...