Source

File: wp-includes/class-wp-network-query.php

private function set_found_networks() {
		global $wpdb;

		if ( $this->query_vars['number'] && ! $this->query_vars['no_found_rows'] ) {
			/**
			 * Filters the query used to retrieve found network count.
			 *
			 * @since 4.6.0
			 *
			 * @param string           $found_networks_query SQL query. Default 'SELECT FOUND_ROWS()'.
			 * @param WP_Network_Query $network_query        The `WP_Network_Query` instance.
			 */
			$found_networks_query = apply_filters( 'found_networks_query', 'SELECT FOUND_ROWS()', $this );

			$this->found_networks = (int) $wpdb->get_var( $found_networks_query );
		}
	}