Which file in wordpress stores database related functions ?

In WordPress, database-related functions are primarily stored in the wp-includes/wp-db.php file. This file contains the wpdb class, which handles all database interactions in WordPress. The wpdb class uses MySQL to execute SQL commands and provides various methods for inserting, updating, deleting, and querying data.

For example, if you need to retrieve data for a specific page, you can use the get_results method provided by the wpdb class. This method allows you to execute arbitrary SQL queries and return results. Here is an example:

php
global $wpdb;
$page_id = 42;
$query = "SELECT * FROM $wpdb->posts WHERE ID = %d";
$page = $wpdb->get_results($wpdb->prepare($query, $page_id));

In this example, we first declare the global variable $wpdb to ensure we can use the WordPress database object. Then we define a query, safely inserting the page ID into the SQL query using the prepare method, and finally execute the query and retrieve the data using the get_results method.

This structure ensures the code's security and flexibility, allowing developers to interact effectively with the WordPress database.