drupal/core/modules/mysql/mysql.module

<?php

/**
 * @file
 * The MySQL module provides the connection between Drupal and a MySQL, MariaDB or equivalent database.
 */

use Drupal\Core\Routing\RouteMatchInterface;

/**
 * Implements hook_help().
 */
function mysql_help($route_name, RouteMatchInterface $route_match) {
  switch ($route_name) {
    case 'help.page.mysql':
      $output = '';
      $output .= '<h3>' . t('About') . '</h3>';
      $output .= '<p>' . t('The MySQL module provides the connection between Drupal and a MySQL, MariaDB or equivalent database. For more information, see the <a href=":mysql">online documentation for the MySQL module</a>.', [':mysql' => 'https://www.drupal.org/docs/core-modules-and-themes/core-modules/mysql-module']) . '</p>';
      return $output;

  }
}