When you want to manipulate your WordPress database from your PHP script, you’ll want to use the wpdb class. This handy utility will give you a convenient way to retrieve the data you need. $wpdb allows you to access core WordPress tables and retrieve information in a modular fashion. However, it may be overkill if you’re only looking to manipulate the data stored in your database. The following are some examples of how to use the wpdb class.
The wpdb class represents the default tables of WordPress. It represents each default table by a custom property. It also has a query method which is designed to handle SQL queries. However, if you need to connect to more than one database, you must create your own object and instantiate it instead. This way, you’ll be safe from any SQL errors and you won’t have to worry about the database being corrupted.
The wpdb class has a global object called $wpdb. You can use it to access and manipulate any of the tables in WordPress. It has its own data structure and creates data objects. It doesn’t access the database directly, but it does use the MySQL system to store all the data you need for your site. If you have a complex query, you can use the wpdb->query() method.