The process of planning and designing a database is one of the most critical phases of any project. A well-planned database design eases the process for future growth while increasing performance in data storage and retrieval. Usually, it's the responsibility of the development team to identify the entities and relationships between these entities. WordPress, on the other hand, is a CMS and hence offers an existing database to handle core features. So, the process of planning a database is not part of the responsibility as a developer in most scenarios. Instead, developers have a tougher task of understanding the core tables and managing the data needs with its limitations. Of course, you can create and use your own database tables for any requirement. But, doing so eliminates the whole purpose of developing on top of WordPress.

The...

The WordPress database structure is designed to store a minimum amount of data required for core features. Therefore, developers need to have a thorough understanding of the existing tables in order to use them effectively to build flexible websites. Let's take a look at the entity relationship diagram of the latest WordPress versions:

As may notice, all the existing tables don't have more than one or two relationships with other tables, and hence understanding and working with the database becomes a simpler task. Now, we are going to look at each database table with important columns, its role, and how it works with other tables. You need to refer to the preceding diagram to visualize the points in our discussion.

In today's world, many of the developers doesn't have in-depth knowledge of WordPress core features and yet, capable of turning your requirement into a working solution. However, these solutions are often based on assumptions, rather than knowing the exact process and data usage under the hood.

Tracking database usage and knowing the exact data needs of any given process is crucial for building flexible and extendable solutions that integrate perfectly with other parts of the site. Let's identify some of the use cases where you need perfect knowledge of data usage in WordPress features:

WordPress offers a powerful backend...

We identified the importance of tracking and knowing the data needs of core features as well as custom features. The next question is how we can track and understand data to avoid potential conflicts. So, we need a method that logs/shows all queries run within a user request. There are numerous ways to track database queries, including premium enterprise tools and the command line. As you are beginning WordPress development, we are going to look at some of the simpler and useful methods that expand your knowledge.

This is one of the simpler and must-know methods as a developer. Both MySQL and MariaDB allow us to create a log file where we can...

At this point, you should be able to configure and track database usage for both backend and frontend user requests. In this section, we will be looking at the usage of database in the most common WordPress features, and understand the need for storing the specified data.

Being the most frequently used feature in WordPress sites, you need thorough understanding of the database usage. First, you need to go to Posts | Add New section and clear the existing query logs. Then, you can add the data and publish a post to track the database usage. The Post creation screen offers wide range of features and hence database usage may vary based on the amount of options...

Multisite network is a feature that allows creation of multiple sites within the same WordPress installation, while sharing the available resources. Developers moving to WordPress from pure PHP development may be unfamiliar with this concept. The whole database structure changes in multisite in a way that we can't anticipate. So, it's important to get an idea of how multisite database works in case you are planning to develop multisite compatible plugins and themes. The following is a simple illustration of the changes in multisite compared to single site installations:

As you can see, six new tables have been added to the database and the existing tables have increased. This image only illustrates how tables are connected in multisite environment. However, this not a precise relationship diagram between the tables. Let...

A default WordPress database can be extended by any number of custom tables to suit our project's requirements. The only thing we have to consider is the creation of custom tables over existing ones. There are two major reasons for creating custom tables:

• Difficulty of matching data to existing tables: Existing database tables are flexible enough to handle many common requirements. However, we need to be wise enough to choose custom tables in certain scenarios. Assume we have a requirement where we need to store user's previous job history. If we consider existing tables, we can only match this requirement to wp_usermeta table as key-value pairs. However, it's extremely difficult to implement proper search for these data by using the same metakey with multiple values. In such requirements, we need a custom table to create predefined...