Queries are used by WordPress to fetch data from the backend database (MySQL), process it or display it on the blog. This data could be anything like blog posts, blog pages, comments or any other content.
For a standard retrieval of data, the wp_query is used. wp_query is a built-in class in WordPress which has methods used to perform many of the key operations in your blog.
- For example, wp_query has methods like get_posts() which is used to get the list of blog posts from the database (along with the post count).
- It also has methods which take variable arguments like querying blog posts based on the Author name/ID, Category name, Tag name etc.
- In simple terms, this is used to display the recent blog posts, the popular blog posts etc.
Also, wp_query() can be used when you have to show counts of data such as comments or have conditional fetching of data or need to loop through data sets to get the desired results. It can also take SQL statements as inputs and interacts with the database accordingly.
Sometimes there are conditions for getting data. In this case, custom queries can be written. Custom queries can be written when there are more complex scenarios such as restriction on the number of posts to be displayed or exclusion of posts or getting of modified search results etc.
In short, the query is a way to fetch data from the backend database (for example, MySQL) used by the WordPress core, themes, plugins.