I'm working on a event tracking system which uses a handful of lookup tables as well as the primary logging table. In a report I'm writing, an object can be selected to view statistics against. The interface shows all objects in order of decreasing importance (ie, hits).
The schema for the two tables (slightly trimmed down, but you get the gist):
CREATE TABLE IF NOT EXISTS `event_log` ( `event_id` int(11) NOT NULL AUTO_INCREMENT, `user_id` int(5) DEFAULT NULL, `object_id` int(5) DEFAULT NULL, `event_date` datetime DEFAULT NULL, PRIMARY KEY (`event_id`), KEY `user_id` (`user_id`), KEY `object_id` (`object_id`) ); CREATE TABLE IF NOT EXISTS `lookup_event_objects` ( `object_id` int(11) NOT NULL AUTO_INCREMENT, `object_desc` varchar(255) NOT NULL, PRIMARY KEY (`object_id`) );
The query I'm having trouble with is below. It works fine with my table of ~100 entries, but the EXPLAIN worries me a little.
explain SELECT el.object_id, leo.object_desc, COUNT(el.object_id) as count_rows FROM event_log el LEFT JOIN lookup_event_objects leo ON leo.object_id = el.object_id GROUP BY el.object_id ORDER BY count_rows DESC, leo.object_desc ASC
Using index; Using temporary; Using filesort
So -- what's wrong with my schema and/or query for MySQL to fall back on
filesort? Or is it as optimized as it can get using ORDER BY?