SHOW PROFILE for the following query:
SELECT `topic`.* FROM `topics` AS `topic`
LEFT OUTER JOIN `topic` AS `topic_helper` ON (`topic`.`id` = `topic_helper`.`id` AND `topic_helper`.`created_on` < `topic`.`created_on`)
GROUP BY `topic`.`id` HAVING COUNT(*) < 3
ORDER BY `topic`.`created_on` DESC;
+--------------------------------+----------+
| Status | Duration |
+--------------------------------+----------+
| starting | 0.000021 |
| Waiting for query cache lock | 0.000004 |
| Waiting on query cache mutex | 0.000004 |
| checking query cache for query | 0.000082 |
| checking permissions | 0.000006 |
| checking permissions | 0.000008 |
| Opening tables | 0.000359 |
| System lock | 0.000018 |
| Waiting for query cache lock | 0.000004 |
| Waiting on query cache mutex | 0.000025 |
| init | 0.000009 |
| checking permissions | 0.000004 |
| checking permissions | 0.000004 |
| checking permissions | 0.000003 |
| checking permissions | 0.000004 |
| checking permissions | 0.000003 |
| checking permissions | 0.000003 |
| checking permissions | 0.000091 |
| optimizing | 0.000022 |
| statistics | 0.000081 |
| preparing | 0.000035 |
| Creating tmp table | 0.000448 |
| Sorting for group | 0.000009 |
| executing | 0.000004 |
| Copying to tmp table | 0.428565 |
| Sorting result | 0.005275 |
| Sending data | 0.000772 |
| end | 0.000008 |
| removing tmp table | 0.002753 |
| end | 0.000009 |
| query end | 0.000010 |
| closing tables | 0.000032 |
| freeing items | 0.000318 |
| logging slow query | 0.000004 |
| cleaning up | 0.000009 |
+--------------------------------+----------+
35 rows in set (0.00 sec)