Create custom table in drupal 8

Create custom table in drupal 8

Creating custom table in drupal 8 is not recommended. Create entity types instead.  
But if you want to Create custom table you can create either by implementing hook_schema or 
else create schema file config/schema/your_custom_module_name.schema.yml  in your module 
(https://www.drupal.org/docs/8/api/configuration-api/configuration-schemametadata). 

( https://drupal.stackexchange.com/questions/219580/best-practice-for-creating-table-in-custom-module  )

1. Implementing  hook_schema in .module file (Not recommended).

/**
 * Implements hook_schema().
 *
 * @todo to be removed this as this is already declared in inactive.install file(confirm)
 *
 */
function inactive_user_schema() {
  $schema['inactive_users'] = array(
    'description' => 'The base table for inactive_users.',
    'fields' => array(
      'uid' => array(
        'description' => 'The primary identifier for a user.',
        'type' => 'int',
        'unsigned' => TRUE,
        'not null' => TRUE,
        'default' => 0,
      ),
      'notified_admin' => array(
        'description' => 'Admin notifier.',
        'type' => 'int',
        'size' => 'tiny',
        'unsigned' => TRUE,
        'not null' => TRUE,
        'default' => 0,
      ),
      'notified_user' => array(
        'description' => 'User notifier.',
        'type' => 'int',
        'size' => 'tiny',
        'unsigned' => TRUE,
        'not null' => TRUE,
        'default' => 0,
      ),
      'warned_user_block_timestamp' => array(
        'description' => 'Timestamp warning.',
        'type' => 'int',
        'unsigned' => TRUE,
        'not null' => TRUE,
        'default' => 0,
      ),
      'notified_user_block' => array(
        'description' => 'User block warning.',
        'type' => 'int',
        'size' => 'tiny',
        'unsigned' => TRUE,
        'not null' => TRUE,
        'default' => 0,
      ),
      'notified_admin_block' => array(
        'description' => 'Timestamp warning.',
        'type' => 'int',
        'size' => 'tiny',
        'unsigned' => TRUE,
        'not null' => TRUE,
        'default' => 0,
      ),
      'warned_user_delete_timestamp' => array(
        'description' => 'Timestamp warning.',
        'type' => 'int',
        'unsigned' => TRUE,
        'not null' => TRUE,
        'default' => 0,
      ),
      'protected' => array(
        'description' => 'Timestamp warning.',
        'type' => 'int',
        'size' => 'tiny',
        'unsigned' => TRUE,
        'not null' => TRUE,
        'default' => 0,
      ),
      'inactive_user_notification_flag' => array(
        'description' => 'Inactive user notification flag.',
        'type' => 'int',
        'not null' => TRUE,
        'default' => 1,
      ),
    ),
    'primary key' => array('uid'),
  );

  $schema['inactive_user_flag'] = array(
    'description' => 'Inactive user flag.',
    'fields' => array(
      'id' => array(
        'description' => 'The primary key to store unique information.',
        'type' => 'serial',
        'not null' => FALSE,
      ),
      'user_id' => array(
        'description' => 'Storing inactive user id.',
        'type' => 'int',
      ),
      'value' => array(
        'description' => 'Storing inacitve user value.',
        'type' => 'int',
      ),
    ),
    'primary key' => array('id'),

  );

  return $schema;
}

2. other way you have to schema.yml inside config/schema/  follow this link https://www.drupal.org/docs/8/api/configuration-api/configuration-schemametadata