MySQL分组排序取前N条记录以及生成自动数字序列的SQL_MySQL

mysql> SELECT * FROM (SELECT cid,author,COUNT(*) AS number FROM test GROUP BY cid,author) a     -> WHERE      -> 3>(    ->     SELECT COUNT(*)     ->     FROM (SELECT cid,author,COUNT(*) AS number FROM test GROUP BY cid,author) b    ->     WHERE a.cid=b.cid AND a.number<b.number    -> )ORDER BY cid,number DESC;+------+----------------+--------+| cid  | author         | number |+------+----------------+--------+|    1 | test3          |      4 ||    1 | test2          |      3 ||    1 | test1          |      2 ||    2 | test33         |      4 ||    2 | test22         |      3 ||    2 | test11         |      2 ||  200 | 200test_nagios |      1 |+------+----------------+--------+7 rows in set (0.00 sec)