Quoting from the WordPress VIP Development Best Practices:
Remember that the database is not a tool box. Although you might be
able to perform a lot of work on the database side, your code will
scale much better by keeping database queries simple and performing
necessary calculations and logic in PHP.
That said, you might just try to get all non-admin users and then add the current user to the results, if that user has admin capabilities.
You can easily achieve this using higher-level WordPress functions:
<?php
/* get all non-admin users */
$args = array(
'meta_key' => 'wp_capabilities',
'meta_value' => 'Administrator', /* you better check for a capability, not a role */
'meta_compare' => 'NOT LIKE'
);
$user_query = new WP_User_Query( $args );
/* if current user is admin, get its user object */
$current_admin_user = current_user_can( 'activate_plugins' ) ? wp_get_current_user() : null;
/* merge non-admin users with current admin-user */
$results = $user_query->get_results();
$results[] = $current_admin_user;
/* update the user query */
$user_query->__set( 'results', $results );
$user_query->__set( 'total_users', count( $results ));
/* do whatever you want */
print_r($user_query);