Source

File: wp-admin/includes/deprecated.php

public function prepare_query() {
		global $wpdb;
		$this->first_user = ($this->page - 1) * $this->users_per_page;

		$this->query_limit = $wpdb->prepare(" LIMIT %d, %d", $this->first_user, $this->users_per_page);
		$this->query_orderby = ' ORDER BY user_login';

		$search_sql = '';
		if ( $this->search_term ) {
			$searches = array();
			$search_sql = 'AND (';
			foreach ( array('user_login', 'user_nicename', 'user_email', 'user_url', 'display_name') as $col )
				$searches[] = $wpdb->prepare( $col . ' LIKE %s', '%' . like_escape($this->search_term) . '%' );
			$search_sql .= implode(' OR ', $searches);
			$search_sql .= ')';
		}

		$this->query_from = " FROM $wpdb->users";
		$this->query_where = " WHERE 1=1 $search_sql";

		if ( $this->role ) {
			$this->query_from .= " INNER JOIN $wpdb->usermeta ON $wpdb->users.ID = $wpdb->usermeta.user_id";
			$this->query_where .= $wpdb->prepare(" AND $wpdb->usermeta.meta_key = '{$wpdb->prefix}capabilities' AND $wpdb->usermeta.meta_value LIKE %s", '%' . $this->role . '%');
		} elseif ( is_multisite() ) {
			$level_key = $wpdb->prefix . 'capabilities'; // WPMU site admins don't have user_levels.
			$this->query_from .= ", $wpdb->usermeta";
			$this->query_where .= " AND $wpdb->users.ID = $wpdb->usermeta.user_id AND meta_key = '{$level_key}'";
		}

		do_action_ref_array( 'pre_user_search', array( &$this ) );
	}