How To Divide Query Output into Groups? - MySQL FAQs - SQL SELECT Query Statements with GROUP BY

You can divide query output into multiple groups with the GROUP BY clause. It allows you specify a column as the grouping criteria, so that rows with the same value in that column will be considered as a single group. When the GROUP BY clause is specified, the select statement can only be used to return group level information. The following script gives you a good GROUP BY example:

mysql> SELECT tag, COUNT(*), MIN(created), AVG(counts) 
   FROM fyi_links GROUP BY tag;
+------+----------+---------------------+-------------+
| tag  | COUNT(*) | MIN(created)        | AVG(counts) |
+------+----------+---------------------+-------------+
| DBA  |        3 | 2005-01-01 00:00:00 |      3.6667 |
| DEV  |        2 | 2004-01-01 00:00:00 |      4.0000 |
| SQA  |        2 | 2003-01-01 00:00:00 |      7.0000 |
+------+----------+---------------------+-------------+
3 rows in set (0.07 sec)