I&#39;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&#39;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&#39;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

Returns: 
`Using index; Using temporary; Using filesort`

So -- what&#39;s wrong with my schema and/or query for MySQL to fall back on `temporary` and `filesort`?  Or is it as optimized as it can get using ORDER BY? 

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Using index, using temporary, using filesort - how to fix this?