Beginners Guild to Understanding The WordPress Database
To extend WordPress, a developer needs to have a foundational understanding of the WordPress database as well as knowledge of how to interact with and manipulate the data stored there. In this session, we’ll take a high-level overview of the WordPress database, review the default ways to interact with the core schema and data, as well as learn how to add and use custom tables for additional functionality.
Introduction
In this tutorial, you’ll be learning about the WordPress database. You will learn about the different tables in the WordPress database, what they’re used for, and learn about core WordPress functions to use when you want to interact with these database tables.
The WordPress Database
WordPress uses a database to store, retrieve, and display all the content that you create on your website. This includes posts, pages, comments, and more. The database is also used to store information about your website’s users, and various site options that power your site. WordPress uses a database management system called MySQL. MySQL is a free, open-source database management system that is used by many popular web applications.
Interacting with your WordPress database
There are a few ways to interact directly with your WordPress database. The majority of local development environments or hosting companies use a free tool called phpMyAdmin. phpMyAdmin is a web-based tool that allows you to interact with your WordPress database using a web browser.
Database Tables
The WordPress database is made up of many tables. Each table stores a different type of data for your website. Each table has the same prefix, which is defined in the wp-config file. By default, the prefix is wp_ but you can change this to anything you like during the WordPress installation process. Let’s start by looking at the most important tables for managing content.
wp_posts and wp_postmeta
The wp_posts table is probably the most important in a WordPress site, and stores information about your website’s posts, pages, or any other custom post type. Each row in the wp_posts table represents a single post. The wp_postmeta table allows you to store additional information about each post. The post meta are also often referred to as custom fields.
wp_comments and wp_commentmeta
The wp_comments table stores information about the comments on your posts and pages. Whenever someone comments on a post or page, this table is where that comment is stored. Each row in the wp_comments table represents a single comment. The wp_commentmeta table can store additional information about each comment.
wp_user and wp_usermeta
The wp_users table stores all the information about your website’s users. Each row in the wp_users table represents a single user. Like other meta tables, the wp_usermeta table can store additional information about each user.
Functions to interact with posts, comments, and users
For all WordPress database tables, there are functions that you can use to interact with that table. These functions form part of the WordPress Database API. All of these functions can be found by using the search feature in the WordPress developer documentation, under Code Reference. Generally, the functions that you can use to interact with the WordPress database all follow a similar pattern. There is an insert function, an update function, and a delete function. These usually have the same name, with the prefix wp_ followed by the action, followed by the name of the table. Let’s look at these functions for posts for example:
- wp_insert_post is the function to create a new post
- wp_update_post is the function to update an existing post
- wp_delete_post is the function to delete a post
Then there are usually functions to fetch either all the records from a table or a single record. These usually have the same name, with the prefix get_ followed by either the singular or plural name of the table. So for example get_posts is the function to fetch a collection of posts. And get_post is the function to fetch a singular post. Each of these functions typically has several parameters that you can use to filter the results that are returned. Then, there are also functions to interact with any meta tables, usually to insert, update, or delete meta fields. These usually have the same name, with the action, followed by the singular name of the table, followed by _meta. So for example for posts, add_post_meta is the function to insert a meta field. Similarly,update_post_meta is the function to update a meta field and delete_post_meta is the function to delete a meta field.
wp_terms, wp_termmeta, wp_term_relationships, and wp_term_taxonomy
The wp_terms, wp_termmeta, wp_term_relationships, and wp_term_taxonomy tables are the tables that manage the categories and tags in your WordPress site. The wp_terms table stores information about your website’s terms. Each row in the wp_terms table represents a single term. Under the hood, categories and tags are both terms. What determines whether they are a category or a tag is the taxonomy that they are associated with, which is stored in the wp_term_taxonomy table. The wp_term_relationships table stores the relationships between terms and their parent objects, be that a post, page, or custom post type. Finally, The wp_termmeta table can store additional information about each term.
Functions to interact with terms and taxonomies
Similar to the functions to interact with posts, comments, and users, there are also functions to interact with terms and taxonomies, which can be found by searching the WordPress Code Reference for terms or taxonomy.
wp_options
The wp_options table stores information about your website’s settings. Each row in the wp_options table represents a specific setting. For example, the site URL option stores the URL of your website, and the blog description option stores the tagline of your website. The wp_options table also stores information about your website’s active theme and active plugins. Data is stored in the wp_options table using a key-value format. The key is the name of the option, and the value is the value of the option. It is also possible to store serialized data in the wp_options table. Serialized data is a string that contains multiple values. Serialized data is often used to store arrays and objects of data. A good example of this is the list of active plugins, which is stored as a serialized array.
Functions to interact with options
The Options API is typically used along with the Settings API to create settings pages for the WordPress dashboard, either via core, plugins, or themes. The Options API provides functions to interact with the wp_options table, like add_option, update_option, and delete_option.
wp_links
The wp_links table stores information about your website’s links. Each row in the wp_links table represents a single link. Links were a feature that was removed from WordPress in version 3.5. However, the wp_links table is still included in the WordPress database for backward compatibility, and it is still possible to add links to your website using the Links Manager plugin.