A query is a formalized computer command that makes an inquiry from a database. In WordPress, a query is always written in the PHP programming language and used to access information from a MySQL database. In essence, any interaction with the database is a query, whether that’s adding data, updating data, deleting data, requesting data, selecting data, or inserting data.
Every single action that happens on a WordPress site involves queries. For example, when a visitor arrives at your site, WordPress will query the database to retrieve all of the information necessary to display your site, including the name of your website, the background images, content from posts and pages, and style information.
Furthermore, every time a visitor interacts with your site, whether it’s liking or rating a page or post, updating or creating a profile, or leaving a comment, this will trigger WordPress to send queries to the database in order to execute these actions. If you’re not interested in doing any programming or coding, then you don’t have to worry about how queries work as WordPress will take care of this for you automatically.
For developers, WordPress has a number of built-in functions which allow specialized queries of the database, including retrieving recent posts, retrieving all posts, and retrieving comments. There are a number of formalized queries that you can use to retrieve and/or organize certain data such as recent posts from a specific category or containing a certain tag.
Queries can also be used to create widgets that will sort or display information based on a number of different parameters, including status (published, draft, etc), tags, category, tags, and many others. You can also use queries to create special, custom pages that are designed to display a specific range of content.